Transmission device, reception device, transmission method, and reception method

ABSTRACT

A transmission device includes a first mapper, a second mapper, a converter, a superposer, and a transmitter. The first mapper is configured to map a first bit stream of a first data series to generate a first modulated symbol stream. The second mapper is configured to map a second bit stream of a second data series to generate a second modulated symbol stream. The first modulated symbol stream and the second modulated symbol stream are representable on a complex plane extending in a first direction and a second direction. The converter is configured to convert the second modulated symbol stream in accordance with the first modulated symbol stream only in the first direction on the complex plane. The superposer is configured to superpose the first modulated symbol stream and the second modulated symbol stream converted by the converter, at an amplitude ratio, to generate a multiplexed signal.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.16/731,573, filed Dec. 31, 2019, which is a continuation of U.S.application Ser. No. 16/270,930, filed Feb. 8, 2019, now U.S. Pat. No.10,567,016, which is a U.S. continuation application of PCTInternational Patent Application Number PCT/JP2017/027831 filed on Aug.1, 2017, claiming the benefit of priority of U.S. Provisional PatentApplication No. 62/374,227 filed on Aug. 12, 2016, the entire contentsof which are hereby incorporated by reference.

BACKGROUND 1. Technical Field

The present disclosure relates to a transmission device, a receptiondevice, a transmission method, and a reception method.

2. Description of the Related Art

A multiplexing scheme utilizing superposition coding is known as ascheme to multiplex and send a plurality of data series (Seokhyun YOONand Donghee KIM, Performance of Superposition Coded Broadcast/UnicastService Overlay System, IEICE Transactions on Communications, vol.E91-B, No. 9). Other known multiplexing schemes include time divisionmultiplexing and frequency division multiplexing (Thomas M. Cover,Broadcast Channels, IEEE Transactions on Information Theory, vol. IT-18,No. 1).

Compared to time division multiplexing and frequency divisionmultiplexing, the multiplexing scheme utilizing superposition coding issuited to multiplexing a plurality of data series that are required tohave different levels of noise tolerance (receiver tolerance). Themultiplexing scheme utilizing superposition coding is also termed aslayer division multiplexing. The multiplexing scheme utilizingsuperposition coding applied to multiple access is also known asnon-orthogonal division multiple access (NOMA).

In the multiplexing scheme utilizing superposition coding, atransmission device superposes a plurality of modulated symbols, whichare obtained by modulating each of a plurality of data series, usingpredetermined power allocation, and transmits the superposed modulatedsymbols. A reception device sequentially demodulates the modulatedsymbols that are multiplexed by superposition coding, starting withmodulated symbols in a layer with high noise tolerance until thecompletion of demodulating modulated symbols in a layer to which adesired data series belongs.

More specifically, the reception device demodulates the modulatedsymbols in a layer with the highest noise tolerance to estimate a dataseries. When a desired data series is yet to be estimated, the receptiondevice generates a replica of each modulated symbol from another dataseries that has been estimated to cancel the replica from the receivedsignal, and demodulates modulated symbols in a layer with the secondhighest noise tolerance to estimate another data series. The receptiondevice repeats these processes until the desired data series isestimated.

SUMMARY

According to an aspect of the present disclosure, a transmission deviceincludes a first mapper, a second mapper, a converter, a superposer, anda transmitter. The first mapper is configured to map a first bit streamof a first data series to generate a first modulated symbol stream. Thesecond mapper is configured to map a second bit stream of a second dataseries to generate a second modulated symbol stream. The first modulatedsymbol stream and the second modulated symbol stream are representableon a complex plane extending in a first direction and a second directionperpendicular to the first direction. The converter is configured toconvert the second modulated symbol stream in accordance with the firstmodulated symbol stream only in the first direction on the complexplane. The superposer is configured to superpose the first modulatedsymbol stream and the second modulated symbol stream converted by theconverter, at an amplitude ratio, to generate a multiplexed signal. Thetransmitter is configured to transmit the multiplexed signal.

Further merits and advantageous effects in one aspect of the presentdisclosure will become apparent from the following description anddrawings. These merits and advantageous effects are provided by thecharacteristics described in the following description and drawings.However, not all of these merits and advantageous effects are requiredto be provided, and thus one or more of these merits and advantageouseffects may be provided by one or more of the characteristics describedin the description and drawings.

BRIEF DESCRIPTION OF DRAWINGS

These and other objects, advantages and features of the disclosure willbecome apparent from the following description thereof taken inconjunction with the accompanying drawings that illustrate a specificembodiment of the present disclosure.

FIG. 1 is a block diagram of an example configuration of a transmissiondevice according to Embodiment 1;

FIG. 2 is a block diagram of an example configuration of a receptiondevice according to Embodiment 1;

FIG. 3 is a diagram showing transmission capacities in superpositioncoding;

FIG. 4 is a diagram showing an example QPSK constellation;

FIG. 5 is a diagram showing an example non-uniform constellation;

FIG. 6 is a diagram showing transmission capacities in superpositioncoding using QPSK and Nu-256QAM;

FIG. 7 is a block diagram of a first example configuration of areception device according to Embodiment 2;

FIG. 8 is a diagram showing an example superposition constellation;

FIG. 9 is a flowchart of a first example of reception operationsaccording to Embodiment 2;

FIG. 10 is a diagram showing an example result of simulation to comparesequential decoding and parallel decoding in superposition coding;

FIG. 11 is a block diagram of a second example configuration of thereception device according to Embodiment 2;

FIG. 12 is a flowchart of a second example of reception operationsaccording to Embodiment 2;

FIG. 13 is a block diagram of a first example configuration of atransmission device according to Embodiment 3;

FIG. 14 is a block diagram of a second example configuration of thetransmission device according to Embodiment 3;

FIG. 15 is a block diagram of a third example configuration of thetransmission device according to Embodiment 3;

FIG. 16 is a block diagram of a first example configuration of areception device according to Embodiment 3;

FIG. 17 is a block diagram of a second example configuration of thereception device according to Embodiment 3;

FIG. 18 is a block diagram of a third example configuration of thereception device according to Embodiment 3;

FIG. 19 is a block diagram of a fourth example configuration of thereception device according to Embodiment 3;

FIG. 20 is a diagram showing an example of a variation superpositionconstellation according to Embodiment 3;

FIG. 21 is a flowchart of an example of transmission operationsaccording to Embodiment 3;

FIG. 22 is a flowchart of an example of reception operations accordingto Embodiment 3;

FIG. 23 is a diagram showing an example result of simulation to comparesequential decoding and parallel decoding in a variation ofsuperposition coding;

FIG. 24 is a block diagram showing a first example configuration of atransmission device according to Embodiment 4;

FIG. 25 is a block diagram showing a second example configuration of thetransmission device according to Embodiment 4;

FIG. 26 is a block diagram showing a third example configuration of thetransmission device according to Embodiment 4;

FIG. 27 is a block diagram showing a first example configuration of areception device according to Embodiment 4;

FIG. 28 is a block diagram showing a second example configuration of thereception device according to Embodiment 4;

FIG. 29 is a block diagram showing a third example configuration of thereception device according to Embodiment 4;

FIG. 30 is a block diagram showing a fourth example configuration of thereception device according to Embodiment 4;

FIG. 31 is a diagram showing an example of a BPSK constellation;

FIG. 32 is a diagram showing a first example of a variationsuperposition constellation according to Embodiment 4;

FIG. 33 is a flowchart of an example of transmission operationsaccording to Embodiment 4;

FIG. 34 is a flowchart of an example of reception operations accordingto Embodiment 4;

FIG. 35 is a diagram showing an example of a constellation based on PAM;and

FIG. 36 is a diagram showing a second example of the variationsuperposition constellation according to Embodiment 4.

DETAILED DESCRIPTION OF THE EMBODIMENTS

In some cases, the multiplexing scheme utilizing superposition codingfails to efficiently process a plurality of data series.

For example, the multiplexing scheme utilizing superposition coding issubjected to processing delays due to the process that requiressequential decoding of a plurality of multiplexed data series.Furthermore, the multiplexing scheme utilizing superposition codingrequires the reception device to include an arithmetic resource, etc.for re-modulating a forward decoded data series. The reception device isalso required to include a memory resource, etc. for holding receivedsymbols used to decode the subsequent data series, from when theprevious data series is decoded and re-modulated until when a modulatedsymbol stream of the previous data series is obtained.

Moreover, the multiplexing scheme utilizing superposition coding maysuffer a decrease in transmission capacity due to a plurality ofsuperposed data series affecting each other.

The present disclosure provides exemplary embodiments that solve theabove-described problems involved in the multiplexing scheme utilizingsuperposition coding. The present disclosure, however, also provides anaspect that solves not completely but partially the above-describedproblems, or an aspect that solves a problem different from theabove-described problems.

The following describes in detail the embodiments according to thepresent disclosure with reference to the drawings. Note that thefollowing embodiments, etc. show a comprehensive or specificillustration of the present disclosure. The numerical values, shapes,materials, structural components, the arrangement and connection of thestructural components, steps, the processing order of the steps, etc.shown in the following embodiments, etc. are mere examples, and thus arenot intended to limit the present disclosure. Of the structuralcomponents described in the following embodiments, etc. structuralcomponents not recited in any one of the independent claims thatindicate the broadest concepts of the present disclosure will bedescribed as optional structural components.

Also note that encoding may mean error control coding. Error controlcoding is also referred to as error-correcting coding. Also, decodingmay mean error control decoding. Error control decoding is also referredto as error-correcting decoding or error correction. Also, unknown maymean undetermined, and transmission may mean sending.

Embodiment 1

The present embodiment describes multiplexing a plurality of data seriesonto a plurality of layers by a multiplexing scheme utilizingsuperposition coding, and transmitting the multiplexed data series.

To simplify the description without loss of generality, the presentembodiment and other embodiments describe an example in which two dataseries are multiplexed onto two different layers to be transmitted.However, the multiplexing scheme described in the present embodiment andother embodiments is applicable to three or more data series multiplexedonto three or more different layers to be transmitted.

Also, the present embodiment and other embodiments use a first layer towhich a first data series belongs as a layer with higher noise tolerancethan a second layer to which a second data series belongs.

FIG. 1 shows an example configuration of transmission device 100 thatmultiplexes two data series onto two layers by superposition coding, andtransmits the multiplexed data series. The configuration and operationof transmission device 100 will be described with reference to FIG. 1.

Transmission device 100 includes encoder 111, interleaver 112, mapper113, multiplier 114, encoder 121, interleaver 122, mapper 123,multiplier 124, adder 130, and radio frequency unit (RF unit) 140. Thesestructural components may also be implemented as dedicated orgeneral-purpose circuits. Multiplier 114, multiplier 124, and adder 130can also be represented collectively as a superposer. RF unit 140 canalso be represented as a transmitter. RF unit 140 may include anantenna.

Encoder 111 encodes an inputted first data series on the basis of afirst error control coding scheme to generate a first bit stream.Interleaver 112 permutes the bits in the first bit stream generated byencoder 111 on the basis of a first permutation rule. Such permutationis also referred to as interleaving.

Mapper 113 maps the first bit stream permuted by interleaver 112 inaccordance with a first mapping scheme (a first modulation scheme) togenerate a first modulated symbol stream that includes a plurality offirst modulated symbols. In the mapping in accordance with the firstmapping scheme, mapper 113 maps each group of bits that includes a firstnumber of bits in the first bit stream onto one of the signal points ina first constellation, in accordance with the values of such a group ofbits.

Encoder 121 encodes an inputted second data series on the basis of asecond error control coding scheme to generate a second bit stream.Interleaver 122 permutes the bits in the second bit stream generated byencoder 121 on the basis of a second permutation rule. Such permutationis also referred to as interleaving.

Mapper 123 maps the second bit stream permuted by interleaver 122 inaccordance with a second mapping scheme (a second modulation scheme) togenerate a second modulated symbol stream that includes a plurality ofsecond modulated symbols. In the mapping in accordance with the secondmapping scheme, mapper 123 maps each group of bits that includes asecond number of bits in the second bit stream onto one of the signalpoints in a second constellation, in accordance with the values of sucha group of bits.

When a mapping scheme used is PSK modulation such as BPSK and QPSK, orQAM modulation such as 16QAM and 64QAM, each modulated symbol can berepresented by a complex number, for example, with the real partrepresenting the magnitude of the in-phase component and the imaginarypart representing the magnitude of the orthogonal component. Meanwhile,when a mapping scheme used is PAM modulation, each modulated symbol canbe represented by a real number.

Multiplier 114 multiplies each first modulated symbol in the firstmodulated symbol stream by first amplitude coefficient a₁. Multiplier124 multiplies each second modulated symbol in the second modulatedsymbol stream by second amplitude coefficient a₂. Adder 130 superposesfirst modulated symbols multiplied by first amplitude coefficient a₁ andsecond modulated symbols multiplied by second amplitude coefficient a₂to generate a superposed modulated symbol stream that includes aplurality of superposed modulated symbols.

RF unit 140 sends the generated superposed modulated symbol stream as asignal. More specifically, RF unit 140 generates, from the superposedmodulated symbol stream generated by adder 130, a radio-frequency signalas a signal corresponding to the superposed modulated symbol stream tosend such a radio-frequency signal from the antenna.

Stated differently, the superposer constituted by multiplier 114,multiplier 124, and adder 130 superposes the first modulated symbolstream and the second modulated symbol stream at a predeterminedamplitude ratio, thereby generating a multiplexed signal into which thefirst data series and the second data series are multiplexed.Subsequently, RF unit 140 sends the multiplexed signal. Note that themultiplexed signal corresponds to the superposed modulated symbolstream. Also note that the predetermined amplitude ratio may be 1:1, andthat the multiplication may be omitted.

FIG. 2 shows an example configuration of reception device 200 capable ofreceiving and sequentially decoding the signal on which two data seriesare multiplexed onto two layers by superposition coding, and capable ofobtaining (extracting) one of or both of the multiplexed two dataseries. The configuration and operation of reception device 200 will bedescribed with reference to FIG. 2.

Reception device 200 includes RF unit 230, demapper 211, deinterleaver212, decoder 213, encoder 214, interleaver 215, mapper 216, multiplier217, delayer 218, subtractor 219, demapper 221, deinterleaver 222, anddecoder 223. These structural components may also be implemented asdedicated or general-purpose circuits.

Demapper 211, deinterleaver 212, decoder 213, encoder 214, interleaver215, mapper 216, multiplier 217, delayer 218, subtractor 219, demapper221, deinterleaver 222, and decoder 223 can also be representedcollectively as a deriver. RF unit 230 can also be represented as areceiver. RF unit 230 may include an antenna.

Reception device 200 receives by an antenna the multiplexed signal sentfrom transmission device 100, and inputs such a multiplexed signal intoRF unit 230. Stated differently, RF unit 230 receives the multiplexedsignal via the antenna. The multiplexed signal received by RF unit 230is also represented as a received signal, and corresponds to thesuperimposed modulated symbol stream into which the first modulatedsymbol stream and the second modulated symbol stream are multiplexed. RFunit 230 generates a baseband received signal from the radio-frequencyreceived signal.

Demapper 211 demaps the baseband received signal on the basis of thefirst constellation of the first mapping scheme to generate a first bitlikelihood stream. For example, amplitude coefficient a₁ is reflected inthe first constellation for demapping.

Deinterleaver 212 permutes the first bit likelihood stream on the basisof a permutation rule that is a reverse rule of the first permutationrule. Such permutation is also referred to as deinterleaving. Decoder213 performs decoding that is based on the first error control codingscheme by use of the first bit likelihood stream permuted bydeinterleaver 212, and outputs the decoding result as the first dataseries.

Here, of the received signal corresponding to the superposed modulatedsymbol stream, demapper 211 treats the components corresponding to thesecond modulated symbols in the second data series as an unknown signal(noise), and performs demapping on the basis of the first constellationof the first mapping scheme.

When only the first data series is to be obtained, reception device 200terminates the process upon completing the estimation of the first dataseries. Meanwhile, when the second data series is to be obtained inaddition to the first data series, or when only the second data seriesis to be obtained, reception device 200 performs the processes describedbelow to obtain the second data series.

Encoder 214 encodes the first data series obtained by decoder 213 on thebasis of the first error control coding scheme to generate the first bitstream. Interleaver 215 permutes the bits in the first bit streamgenerated by encoder 214 on the basis of the first permutation rule.Such permutation is also referred to as interleaving.

Mapper 216 maps the first bit stream permuted by interleaver 215 inaccordance with the first mapping scheme to generate the first modulatedsymbol stream that includes a plurality of first modulated symbols.Multiplier 217 multiplies the first modulated symbol stream outputted bymapper 216 by first amplitude coefficient a₁.

Delayer 218 delays the received signal outputted from RF unit 230 duringthe time from when RF unit 230 outputs the baseband received signal towhen multiplier 217 outputs the reproduced first modulated symbolstream.

Subtractor 219 subtracts, from the received signal delayed by delayer218, the first modulated symbol stream multiplied by first amplitudecoefficient a₁ by multiplier 217. Through this, subtractor 219 removesthe components corresponding to the first modulated symbols from thereceived signal on which the components corresponding to the firstmodulated symbols, the components corresponding to the second modulatedsymbols, and noise are superposed. Subsequently, subtractor 219 outputsa signal on which the components corresponding to the second modulatedsymbols and noise are superposed as a signal corresponding to the secondmodulated symbol stream.

Demapper 221 demaps the signal outputted from subtractor 219 on thebasis of the second constellation of the second mapping scheme togenerate a second bit likelihood stream. For example, amplitudecoefficient a₂ is reflected in the second constellation for demapping.

Deinterleaver 222 permutes the second bit likelihood stream on the basisof a permutation rule that is a reverse rule of the second permutationrule. Such permutation is also referred to as deinterleaving. Decoder223 decodes the second bit likelihood stream permuted by deinterleaver222 on the basis of the second error control coding scheme, and outputsthe decoding result as the second data series.

Through the above processes, reception device 200 obtains one of or bothof the first data series and the second data series from the signalreceived by the antenna.

<Superposition Coding>

The following describes superposition coding.

Using signal power P_(s)(W), noise power P_(n)(W), and transmissionbandwidth B(Hz), transmission capacity CT (bit/s) is given as theShannon limit by Equation 1.

$\begin{matrix}\left\lbrack {{Math}.\mspace{11mu} 1} \right\rbrack & \; \\{C_{T} = {B \cdot {\log_{2}\left( {1 + \frac{P_{s}}{P_{n}}} \right)}}} & \left( {{Equation}\mspace{14mu} 1} \right)\end{matrix}$

Transmission capacity C(bit/s/Hz) per Hz normalized by the transmissionbandwidth is given by Equation 2.

$\begin{matrix}\left\lbrack {{Math}.\mspace{11mu} 2} \right\rbrack & \; \\{C = {\log_{2}\left( {1 + \frac{P_{s}}{P_{n}}} \right)}} & \left( {{Equation}\mspace{14mu} 2} \right)\end{matrix}$

In the following, “transmission capacity per Hz” will be simply referredto as “transmission capacity”.

In superposition coding of the first data series and the second dataseries, signal power P_(s1)(W) of the first layer corresponding to thefirst data series, signal power P_(s2) (W) of the second layercorresponding to the second data series, and the entire signal powerP_(s)(W) satisfy: P_(s)=P_(s1)+P_(s2).

When demodulating the first layer, reception device 200 regards thecomponents of the modulated symbols in the second layer as unknowncomponents superposed on the modulated symbols in the first layer, i.e.,noise. As such, transmission capacity C₁ of the first layer is given byEquation 3.

$\begin{matrix}\left\lbrack {{Math}.\mspace{11mu} 3} \right\rbrack & \; \\{C_{1} = {\log_{2}\left( {1 + \frac{P_{s\; 1}}{P_{s\; 2} + P_{n}}} \right)}} & \left( {{Equation}\mspace{14mu} 3} \right)\end{matrix}$

When reception device 200 demodulates the second layer, the componentsof the modulated symbols in the first layer have already been removedfrom the received signal. As such, transmission capacity C₂ of thesecond layer is given by Equation 4.

$\begin{matrix}\left\lbrack {{Math}.\mspace{11mu} 4} \right\rbrack & \; \\{C_{2} = {\log_{2}\left( {1 + \frac{P_{s\; 2}}{P_{n}}} \right)}} & \left( {{Equation}\mspace{14mu} 4} \right)\end{matrix}$

As shown by Equation 5, the total of transmission capacity C₁ of thefirst layer and transmission capacity C₂ of the second layer agrees withthe Shannon limit.

$\begin{matrix}\left\lbrack {{Math}.\mspace{11mu} 5} \right\rbrack & \; \\\begin{matrix}{{C_{1} + C_{2}} = {{\log_{2}\left( {1 + \frac{P_{s1}}{P_{s2} + P_{n}}} \right)} + {\log_{2}\left( {1 + \frac{P_{s2}}{P_{n}}} \right)}}} \\{= {{\log_{2}\left( \frac{P_{s} + P_{n}}{P_{s2} + P_{n}} \right)} + {\log_{2}\left( \frac{P_{s2} + P_{n}}{P_{n}} \right)}}} \\{= {\log_{2}\left( \frac{P_{s} + P_{n}}{P_{n}} \right)}} \\{= {\log_{2}\left( {1 + \frac{P_{s}}{P_{n}}} \right)}}\end{matrix} & \left( {{Equation}\mspace{14mu} 5} \right)\end{matrix}$

In the present embodiment, signal power P_(s1) of the first layercorresponding to the first data series is proportional to the secondpower of first amplitude coefficient a₁, and signal power P_(s2) of thesecond layer corresponding to the second data series is proportional tothe second power of second amplitude coefficient a₂. The allocation ofsignal power to a plurality of layers is determined by an amplitudecoefficient that is multiplied to the modulated symbols of each layer.

FIG. 3 shows an example simulation result of each transmission capacitywhen the ratio between signal power P_(s1) of the first layer and signalpower P_(s2) of the second layer is P_(s1): P_(s2)=2:1. In FIG. 3, thelateral axis represents as dB (decibel) the ratio of signal power P_(s)to noise power P_(n) (SNR), and the vertical axis representstransmission capacity. In FIG. 3, the dot-and-dash line indicatestransmission capacity C₁ of the first layer, the broken line indicatestransmission capacity C₂ of the second layer, and the solid lineindicates the total transmission capacity of transmission capacity C₁ ofthe first layer and transmission capacity C₂ of the second layer.

Note that SNR, which means a ratio of signal power to noise power, isalso referred to as a signal-to-noise power ratio or a signal-to-noiseratio.

<Non-Uniform Constellation>

Transmission device 100 according to the present embodiment can employany mapping scheme for each of the first mapping scheme and the secondmapping scheme. Reception device 200 demodulates the first layer, withthe second modulated symbols of the second layer remaining unknown. Assuch, a mapping scheme such as QPSK, for example, that mainly supports alow SNR is suitable as the first mapping scheme.

FIG. 4 shows an example QPSK constellation. More specifically, four QPSKsignal points are plotted in the complex plane, with the lateral axisrepresenting the real part (the real component) and the vertical axisrepresenting the imaginary part (the imaginary component). In QPSK, agroup of bits (00, 01, 10, or 11) is associated with a modulated symbolindicating a complex number on the basis of the constellation shown inFIG. 4.

Meanwhile, the second layer is demodulated with the modulated symbols inthe first layer having been removed. As such, the second mapping schememay be a mapping scheme that utilizes multilevel constellationsupporting a high SNR.

Non-uniform constellations as disclosed in J. Zoellner and N. Loghin,Optimization of High-order Non-uniform QAM Constellations, IEEEInternational Symposium on Broadband Multimedia Systems and Broadcasting2013 have received recent attention as multilevel constellations. Unlikeconventional uniform constellations that include uniformly spaced signalpoints, such as a QAM constellation, a non-uniform constellationincludes ununiformly spaced signal points. In some cases, a mappingscheme using a non-uniform constellation improves the transmissioncapacity compared to a mapping scheme using a uniform constellation.

FIG. 5 shows an example non-uniform constellation including 256 signalpoints (Nu-256QAM). In FIG. 5, 256 non-uniform constellation signalpoints are plotted in the complex plane, with the lateral axisrepresenting the real part and the vertical axis representing theimaginary part.

The following describes an example of using QPSK shown in FIG. 4 as thefirst mapping scheme and Nu-256QAM shown in FIG. 5 as the second mappingscheme in the multiplexing scheme that utilizes superposition coding.

FIG. 6 shows an example simulation result of each transmission capacitywhen the ratio between signal power P_(s1) of the first layer and signalpower P_(s2) of the second layer is P_(s1): P_(s2)=2:1. In FIG. 6, thelateral axis represents as dB (decibel) the ratio of signal power P_(s)to noise power P_(n) (SNR), and the vertical axis representstransmission capacity. In FIG. 6, the dot-and-dash line indicatestransmission capacity C₁ of the first layer, and the broken lineindicates transmission capacity C₂ of the second layer. A combination ofQPSK and Nu-256QAM achieves a transmission capacity that is close to thelimit shown in FIG. 3.

As described above, transmission device 100 according to the presentembodiment is capable of highly efficient multiplexing and transmissionof a plurality of data series by a multiplexing scheme utilizingsuperposition coding. Reception device 200 is capable of receiving aplurality of data series that have been multiplexed in a highlyefficient manner by the multiplexing scheme utilizing superpositioncoding. Transmission device 100 and reception device 200 are alsocapable of increasing the transmission capacity by use of a non-uniformconstellation.

Note that permutation (interleaving and deinterleaving) reduces theeffects that may be caused when successive errors occur. Permutation(interleaving and deinterleaving) also controls the correspondence amongbits included in codewords in error correcting coding, modulatedsymbols, and bits included in such modulated symbols. However, suchpermutation (interleaving and deinterleaving) may be omitted.

Stated differently, interleaver 112 and interleaver 122 are optionalstructural components, and thus may not be included in transmissiondevice 100. Similarly, deinterleaver 212, interleaver 215, anddeinterleaver 222 are optional structural components, and thus may notbe included in reception device 200.

Interleaving and deinterleaving, however, make a pair. As such, whentransmission device 100 includes interleaver 112 and interleaver 122,reception device 200 basically includes deinterleaver 212, interleaver215, and deinterleaver 222. Meanwhile, when transmission device 100 doesnot include interleaver 112 and interleaver 122, reception device 200does not include deinterleaver 212, interleaver 215, and deinterleaver222.

Also, amplitude coefficient a₁ may be reflected in the mapping performedby mapper 216 of reception device 200. In such a case, reception device200 may omit the multiplication, and thus may not include multiplier217.

Error control coding on the first data series and the second data seriesmay be performed by an external device that is different fromtransmission device 100. In such a case, transmission device 100 mayomit the error control coding, and may not include encoder 111 andencoder 121.

Embodiment 2

<Parallel Decoding of Signal Obtained by Superposition Coding>

The present embodiment describes a reception method for paralleldecoding of a signal obtained by superposition coding. The configurationof the transmission device is the same as the configuration oftransmission device 100 shown in FIG. 1, and thus will not be described.In parallel decoding in superposition coding, the reception devicetreats the components of the modulated symbol stream in the first layeras an unknown signal (noise) to decode the second layer, withoutremoving the components of the modulated symbol stream in the firstlayer included in the received signal.

FIG. 7 shows an example configuration of reception device 300 capable ofreceiving and performing parallel decoding on the signal on which twodata series are multiplexed onto two layers by superposition coding, andcapable of obtaining one of or both of the multiplexed two data series.The configuration and operation of reception device 300 will bedescribed with reference to FIG. 7.

Reception device 300 includes RF unit 330, demapper 310, deinterleaver312, decoder 313, deinterleaver 322, and decoder 323. These structuralcomponents may also be implemented as dedicated or general-purposecircuits. Demapper 310, deinterleaver 312, decoder 313, deinterleaver322, and decoder 323 can also be represented collectively as a deriver.RF unit 330 can also be represented as a receiver. RF unit 330 mayinclude an antenna.

Reception device 300 receives by an antenna the multiplexed signal sentfrom transmission device 100, and inputs such a multiplexed signal intoRF unit 330. Stated differently, RF unit 330 receives the multiplexedsignal via the antenna. The multiplexed signal received by RF unit 330is also represented as a received signal. RF unit 330 generates abaseband received signal from the radio-frequency received signal.

Demapper 310 demaps the baseband received signal to generate the firstbit likelihood stream and the second bit likelihood stream. For example,demapper 310 performs such demapping on the basis of a superpositionconstellation that shows the arrangement of the signal points ofsuperposed modulated symbols obtained by superposing the first modulatedsymbols and the second modulated symbols by superposition coding.

The superposition constellation is determined in accordance with thefirst constellation of the first mapping scheme, the secondconstellation of the second mapping scheme, first amplitude coefficienta₁, first amplitude coefficient a₂, etc.

FIG. 8 shows an example superposition constellation, which is morespecifically a combination of the QPSK constellation shown in FIG. 4 andthe Nu-256QAM constellation shown in FIG. 5. Even more specifically, theNu-256QAM constellation (256 signal points) is placed on each of thefour regions in the complex plane in accordance with the four signalpoints of the QPSK constellation. These four regions, each correspondingto Nu-256QAM constellation, may partially overlap with each other.

Demapper 310 performs demapping on the basis of the superpositionconstellation as shown in FIG. 8. Stated differently, demapper 310generates the first bit likelihood stream, with the modulated symbolstream of the second layer remaining unknown, and generates the secondbit likelihood stream, with the modulated symbol stream of the firstlayer remaining unknown.

Note that demapper 310 may use the first constellation of the firstmapping scheme to generate the first bit likelihood stream, and may usethe above-described superposition constellation to generate the secondbit likelihood stream.

The first constellation, when used to generate the first bit likelihoodstream, enables demapper 310 to reduce the number of signal points thatshould be considered in generating the first bit likelihood stream,compared to when the superposition constellation is also used togenerate the first bit likelihood stream. This thus enables demapper 310to reduce the number of arithmetic computations.

Demapper 310 corresponds, for example, to the first demapper that demapsthe received signal to generate the first bit likelihood stream and thesecond demapper that demaps the received signal to generate the secondbit likelihood stream. Demapper 310 may include the first demapper thatdemaps the received signal to generate the first bit likelihood streamand the second demapper that demaps the received signal to generate thesecond bit likelihood stream.

Deinterleaver 312 permutes the first bit likelihood stream on the basisof a permutation rule that is a reverse rule of the first permutationrule. Such permutation is also referred to as deinterleaving. Decoder313 decodes the first bit likelihood stream permuted by deinterleaver312 on the basis of the first error control coding scheme, and outputsthe decoding result as the first data series.

Deinterleaver 322 permutes the second bit likelihood stream on the basisof a permutation rule that is a reverse rule of the second permutationrule. Such permutation is also referred to as deinterleaving. Decoder323 decodes the second bit likelihood stream permuted by deinterleaver322 on the basis of the second error control coding scheme, and outputsthe decoding result as the second data series.

Note that permutation (deinterleaving) may be omitted as in the case ofEmbodiment 1. Stated differently, deinterleaver 312 and deinterleaver322 are optional structural components, and thus may not be included inreception device 300.

Interleaving and deinterleaving, however, make a pair. As such, whentransmission device 100 includes interleaver 112 and interleaver 122,reception device 300 basically includes deinterleaver 312 anddeinterleaver 322. Meanwhile, when transmission device 100 does notinclude interleaver 112 and interleaver 122, reception device 300 doesnot include deinterleaver 312 and deinterleaver 322.

FIG. 9 is a flowchart of example operations performed by receptiondevice 300. First, RF unit 330 receives the multiplexed signal intowhich the first data series and the second data series are multiplexed(S101).

Next, demapper 310 demaps the multiplexed signal to generate the firstbit likelihood stream of the first data series (S102). Demapper 310demaps the multiplexed signal to generate the second bit likelihoodstream of the second data series (S103). Deinterleaver 312 maydeinterleave such a generated first bit likelihood stream. Also,deinterleaver 322 may deinterleave such a generated second bitlikelihood stream.

Then, decoder 313 performs error control decoding on the first bitlikelihood stream to derive the first data series (S104). Also, decoder323 performs error control decoding on the second bit likelihood streamto derive the second data series (S105).

Note that processes on the first bit likelihood stream (generation,deinterleaving, and error control decoding) and processes on the secondbit likelihood stream (generation, deinterleaving, and error controldecoding) are basically performed in parallel.

Reception device 300 as shown in FIG. 7 that performs parallel decodinghas lower performance in decoding the second layer than that ofreception device 200 as shown in FIG. 2 that performs sequentialdecoding.

FIG. 10 shows an example simulation result of the transmission capacityof the second layer when the ratio between signal power P_(s1) of thefirst layer and signal power P_(s2) of the second layer is P_(s1):P_(s2)=2:1. In FIG. 10, the lateral axis represents as dB (decibel) theratio of signal power P_(s) to noise power Pn (SNR), and the verticalaxis represents transmission capacity. In FIG. 10, the solid lineindicates the transmission capacity of the second layer when sequentialdecoding is performed, and the broken line indicates the transmissioncapacity of the second layer when parallel decoding is performed.

As FIG. 10 shows, in the decoding of the second layer, parallel decodinginvolves an increased SNR with respect to the same transmission capacityand a decreased transmission capacity with respect to the same SNR,compared to sequential decoding.

As described above, reception device 300 according to the presentembodiment that performs parallel decoding has lower performance indecoding the second data series transmitted on the second layer thanthat of reception device 200 that performs sequential decoding. However,reception device 300 reduces the number of structural componentsrequired for decoding the second layer.

More specifically, reception device 300 eliminates the need for encoder214, interleaver 215, mapper 216, and multiplier 217 that are requiredby reception device 200 shown in FIG. 2 performing sequential decodingto reproduce the modulated symbol stream of the first layer. Receptiondevice 300 also eliminates the need for delayer 218 that delays thereceived signal and subtractor 219 that removes the components of themodulated symbols in the first layer reproduced from the receivedsignal.

The circuit size can be thus reduced. Reception device 300 also requiresa smaller number of arithmetic computations and lower power consumptionthan those required by reception device 200.

Reception device 200 shown in FIG. 2 that performs sequential decodingdemodulates the first layer in the received signal to obtain the firstdata series, generates the first modulated symbol stream from theobtained first data series, and then starts demodulating the secondlayer in the received signal to obtain the second data series.Meanwhile, reception device 300 according to the present embodiment thatperforms parallel decoding is capable of simultaneously obtaining thefirst data series and the second data series in parallel, therebyreducing processing delays.

Alternatively, the reception device may observe the SNR of the receivedsignal to make selection between parallel decoding to be performed whenthe SNR is high and sequential decoding to be performed when the SNR islow.

In such a case, reception device 200 shown in FIG. 2 includes, forexample, a controller that makes selection between sequential decodingand parallel decoding depending on the SNR. Such a controller may beincluded in RF unit 230 or demapper 221. Furthermore, demapper 221 isconfigured to perform demapping based on the superpositionconstellation, which is described as an operation performed by demapper310 shown in FIG. 7, in addition to demapping that is based on thesecond constellation.

Demapper 221 switches between demapping to be performed on the signaloutputted from subtractor 219 on the basis of the second constellationand demapping to be performed on the signal outputted from RF unit 230on the basis of the superposition constellation. For example, demapper221 switches between these demapping operations in accordance with acontrol signal from the controller.

FIG. 11 shows an example configuration of reception device 400 thatselectively performs parallel decoding and sequential decoding.Reception device 400 includes RF unit 430, demapper 411, deinterleaver412, decoder 413, encoder 414, interleaver 415, mapper 416, multiplier417, delayer 418, subtractor 419, demapper 421, deinterleaver 422, anddecoder 423. Structural components of reception device 400 shown in FIG.11 and structural components of reception device 200 shown in FIG. 2 arebasically the same.

However, demapper 421 of reception device 400 performs demapping that isbased on the superposition constellation in addition to demapping thatis based on the second constellation of the second mapping scheme. Forexample, depending on the SNR, demapper 421 switches between demappingto be performed on the signal outputted from subtractor 419 on the basisof the second constellation and demapping to be performed on the signaloutputted from RF unit 430 on the basis of the superpositionconstellation.

Although the example shown in FIG. 11 omits a controller that makesselection between sequential decoding and parallel decoding depending onthe SNR, the controller may be included in demapper 421, in RF unit 430,or in reception device 400 as a new structural component.

FIG. 12 is a flowchart of example operations performed by receptiondevice 400. First, RF unit 430 receives the multiplexed signal intowhich the first data series and the second data series are multiplexed(S201). Then, RF unit 430 determines whether the multiplexed signalsatisfies a predetermined requirement. The predetermined requirement,for example, is that the SNR should be higher than a predeterminedthreshold.

When the multiplexed signal satisfies the predetermined requirement (Yesin S202), demapper 411 demaps the multiplexed signal to generate thefirst bit likelihood stream of the first data series (S203). Also,demapper 421 demaps the multiplexed signal to generate the second bitlikelihood stream of the second data series (S204). Deinterleaver 412may deinterleave such a generated first bit likelihood stream. Also,deinterleaver 422 may deinterleave such a generated second bitlikelihood stream.

Decoder 413 performs error control decoding on the first bit likelihoodstream to derive the first data series (S205). Also, decoder 423performs error control decoding on the second bit likelihood stream toderive the second data series (S206).

These operations (S203 to S206) are basically the same as the operations(S102 to S105) shown in FIG. 9.

Meanwhile, when the multiplexed signal fails to satisfy thepredetermined requirement (No in S202), demapper 411 demaps themultiplexed signal to generate the first bit likelihood stream of thefirst data series (S207). Deinterleaver 412 may deinterleave such agenerated first bit likelihood stream. Then, decoder 413 performs errorcontrol decoding on the first bit likelihood stream to derive the firstdata series (S208).

Next, encoder 414 performs error control coding on the first data seriesto generate the first bit stream (S209). Interleaver 415 may interleavesuch a generated first bit stream. Then, mapper 416 maps the first bitstream to generate the first modulated symbol stream (S210). Multiplier417 may multiply the first modulated symbol stream by amplitudecoefficient a₁.

Delayer 418 delays the multiplexed signal until the first modulatedsymbol stream is generated (S211). Then, subtractor 419 subtracts thefirst modulated symbol stream from the multiplexed signal (S212).

Next, demapper 421 demaps the multiplexed signal from which the firstmodulated symbol stream has been subtracted to generate the second bitlikelihood stream (S213). Deinterleaver 422 may deinterleave such agenerated second bit likelihood stream. Then, decoder 423 performs errorcontrol decoding on the second bit likelihood stream to derive thesecond data series (S214).

Through these operations, reception device 400 performs paralleldecoding when the SNR is high, thereby reducing the number of arithmeticcomputations and power consumption. Reception device 400 also performsparallel decoding when the SNR is high, thereby reducing processingdelays. Meanwhile, reception device 400 performs sequential decodingwhen the SNR is low, thereby increasing the possibility of correctlydecoding the second data series.

Note that the first mapping scheme and the second mapping schemeaccording to the present embodiment are basically the same as the firstmapping scheme and the second mapping scheme according to Embodiment 1.Stated differently, the first constellation and the second constellationaccording to the present embodiment are basically the same as the firstconstellation and the second constellation according to Embodiment 1.Any one of a uniform constellation and a non-uniform constellation maybe used as the second mapping scheme.

Embodiment 3

<Variation of Superposition Coding (Modified Superposition Coding)>

The present embodiment describes a method of multiplexing andtransmitting a plurality of data series by a variation of superpositioncoding (modified superposition coding), which is a modified version ofthe above-described superposition coding.

FIG. 13 shows an example configuration of transmission device 500 thatmultiplexes two data series onto two layers by the variation ofsuperposition coding, and transmits a multiplexed data series. Theconfiguration and operation of transmission device 500 will be describedwith reference to FIG. 13.

Transmission device 500 includes encoder 511, interleaver 512, mapper513, multiplier 514, encoder 521, interleaver 522, mapper 523, converter525, multiplier 524, adder 530, and RF unit 540. These structuralcomponents may also be implemented as dedicated or general-purposecircuits. Multiplier 514, multiplier 524, and adder 530 can also berepresented collectively as a superposer. RF unit 540 can also berepresented as a transmitter. RF unit 540 may include an antenna.

Encoder 511 encodes an inputted first data series on the basis of afirst error control coding scheme to generate a first bit stream.Interleaver 512 permutes the bits in the first bit stream generated byencoder 511 on the basis of a first permutation rule. Such permutationis also referred to as interleaving.

Mapper 513 maps the first bit stream permuted by interleaver 512 inaccordance with a first mapping scheme to generate a first modulatedsymbol stream that includes a plurality of first modulated symbols. Inthe mapping in accordance with the first mapping scheme, mapper 513 mapseach group of bits that includes a first number of bits in the first bitstream onto one of the signal points in a first constellation inaccordance with the values of such a group of bits.

When PSK modulation such as BPSK and QPSK, or QAM modulation such as16QAM and 64QAM is used as the first mapping scheme, each firstmodulated symbol can be represented by a complex number, for example,with the real part representing the magnitude of the in-phase componentand the imaginary part representing the magnitude of the orthogonalcomponent. Meanwhile, when PAM modulation is used as the first mappingscheme, each first modulated symbol can be represented by a real number.

Encoder 521 encodes an inputted second data series on the basis of asecond error control coding scheme to generate a second bit stream.Interleaver 522 permutes the bits in the second bit stream generated byencoder 521 on the basis of a second permutation rule. Such permutationis also referred to as interleaving.

Mapper 523 maps the second bit stream permuted by interleaver 522 inaccordance with a second mapping scheme to generate a second modulatedsymbol stream that includes a plurality of second modulated symbols. Inthe mapping in accordance with the second mapping scheme, mapper 523maps each group of bits that includes a second number of bits in thesecond bit stream onto one of the signal points in a secondconstellation in accordance with the values of such a group of bits.

When PSK modulation such as BPSK and QPSK, or QAM modulation such as16QAM and 64QAM is used as the second mapping scheme, each secondmodulated symbol can be represented by a complex number, for example,with the real part representing the magnitude of the in-phase componentand the imaginary part representing the magnitude of the orthogonalcomponent. Meanwhile, when PAM modulation is used as the second mappingscheme, each second modulated symbol can be represented by a realnumber. Any one of a uniform constellation and a non-uniformconstellation may be used as the second mapping scheme.

Converter 525 converts each second modulated symbol to be superposedwith the corresponding first modulated symbol, on the basis of thevalues of the bits used to generate such a first modulated symbol.Through this, converter 525 converts the second modulated symbol stream.

Multiplier 514 multiplies each first modulated symbol in the firstmodulated symbol stream by first amplitude coefficient a₁. Multiplier524 multiplies, by second amplitude coefficient a₂, each secondmodulated symbol in the second modulated symbol stream converted byconverter 525. Adder 530 superposes first modulated symbols multipliedby first amplitude coefficient a₁ and second modulated symbolsmultiplied by second amplitude coefficient a₂ to generate a superposedmodulated symbol stream that includes a plurality of superposedmodulated symbols.

RF unit 540 sends the generated superposed modulated symbol stream as asignal. More specifically, RF unit 540 generates, from the superposedmodulated symbol stream generated by adder 530, a radio-frequency signalas a signal corresponding to the superposed modulated symbol stream tosend such a radio-frequency signal from the antenna.

Stated differently, the superposer constituted by multiplier 514,multiplier 524, and adder 530 superposes the first modulated symbolstream and the second modulated symbol stream at a predeterminedamplitude ratio, thereby generating a multiplexed signal into which thefirst data series and the second data series are multiplexed.Subsequently, RF unit 540 sends the multiplexed signal. Note that themultiplexed signal corresponds to the superposed modulated symbolstream. Also note that the predetermined amplitude ratio may be 1:1, andthat the multiplication may be omitted.

The following shows an example case in which QPSK is used as the firstmapping scheme to describe the operation of converter 525.

For example, when S₁(t) is the t-th modulated symbol in the firstmodulated symbol stream generated by mapper 513, and b₁(t) and b₂(t) area plurality of bits to be mapped onto SAX modulated symbol S₁(t) isgiven by Equation 6.

$\begin{matrix}\left\lbrack {{Math}.\mspace{11mu} 6} \right\rbrack & \; \\{{S_{1}(t)} = \frac{\left( {{2 \cdot {b_{1}(t)}} - 1} \right) + {i \cdot \left( {{2 \cdot {b_{2}(t)}} - 1} \right)}}{\sqrt{2}}} & \left( {{Equation}\mspace{14mu} 6} \right)\end{matrix}$

Here, i denotes the imaginary unit. Modulated symbol S₁(t) may also begiven by an equation in which one of or both of the (positive/negative)polarities of the real part and the imaginary part of Equation 6 arereversed. Bit b₁(t) is a bit that contributes to the real part ofmodulated symbol S₁(t). Bit b₂(t) is a bit that contributes to theimaginary part of modulated symbol S₁(t).

Converter 525 converts, into S′₂(t), the t-th modulated symbol S₂(t) inthe second modulated symbol stream generated by mapper 523, on the basisof b₁(t) and b₂(t) as shown by Equation 7.[Math. 7]S′ ₂(t)=(−1)^(b) ¹ ^((t)·Re[S) ₂(t)]+i·(−1)^(b) ² ^((t))·Im[S₂(t)]  (Equation 7)

Here, S′₂(t) is the converted t-th modulated symbol in the secondmodulated symbol stream. Re[S₂(t)] is the value of the real part ofS′₂(t), and Im[S₂(t)] is the value of the imaginary part of S₂(t).Modulated symbol S′₂(t) may be given by an equation in which one of orboth of the polarities of the real part and the imaginary part ofEquation 7 are reversed.

As described above, the variation of superposition coding controls thepolarities of the real part and the imaginary part of each secondmodulated symbol in accordance with the values of the bits to be mappedonto the first modulated symbol that is superposed with such a secondmodulated symbol. Note that the polarities of the real part and theimaginary part of each second modulated symbol may be controlled inaccordance with the first modulated symbol that is superposed with sucha second modulated symbol. Also, the polarity of one of the real partand the imaginary part of each second modulated symbol may becontrolled, or the polarities of both the real part and the imaginarypart of each second modulated symbol may be controlled.

FIG. 14 shows an example configuration of transmission device 600 thatmultiplexes two data series onto two layers by the variation ofsuperposition coding, and transmits the multiplexed data series. Theconfiguration of transmission device 600 is different from theconfiguration of transmission device 500. The configuration andoperation of transmission device 600 will be described with reference toFIG. 14.

Transmission device 600 includes encoder 611, interleaver 612, mapper613, multiplier 614, encoder 621, interleaver 622, mapper 623, converter625, multiplier 624, adder 630, and RF unit 640. These structuralcomponents may also be implemented as dedicated or general-purposecircuits. Multiplier 614, multiplier 624, and adder 630 can also berepresented collectively as a superposer. RF unit 640 can also berepresented as a transmitter. RF unit 640 may include an antenna.

Encoder 611 encodes an inputted first data series on the basis of afirst error control coding scheme to generate a first bit stream.Interleaver 612 permutes the bits in the first bit stream generated byencoder 611 on the basis of a first permutation rule. Such permutationis also referred to as interleaving.

Mapper 613 maps the first bit stream permuted by interleaver 612 inaccordance with a first mapping scheme to generate a first modulatedsymbol stream that includes a plurality of first modulated symbols. Inthe mapping in accordance with the first mapping scheme, mapper 613 mapseach group of bits that includes a first number of bits in the first bitstream onto one of the signal points in a first constellation inaccordance with the values of such a group of bits.

Encoder 621 encodes an inputted second data series on the basis of asecond error control coding scheme to generate a second bit stream.Interleaver 622 permutes the bits in the second bit stream generated byencoder 621 on the basis of a second permutation rule. Such permutationis also referred to as interleaving.

Mapper 623 maps the second bit stream permuted by interleaver 622 inaccordance with a second mapping scheme to generate a second modulatedsymbol stream that includes a plurality of second modulated symbols. Inthe mapping in accordance with the second mapping scheme, mapper 623maps each group of bits that includes a second number of bits in thesecond bit stream onto one of the signal points in a secondconstellation in accordance with the values of such a group of bits.

Converter 625 converts each second modulated symbol to be superposedwith the corresponding first modulated symbol, on the basis of thegenerated first modulated symbol. Through this, converter 625 convertsthe second modulated symbol stream.

Multiplier 614 multiplies each first modulated symbol in the firstmodulated symbol stream by first amplitude coefficient a₁. Multiplier624 multiplies, by second amplitude coefficient a₂, each secondmodulated symbol in the second modulated symbol stream converted byconverter 625. Adder 630 superposes first modulated symbols multipliedby first amplitude coefficient a₁ and second modulated symbolsmultiplied by second amplitude coefficient a₂ to generate a superposedmodulated symbol stream that includes a plurality of superposedmodulated symbols.

RF unit 640 sends the generated superposed modulated symbol stream as asignal. More specifically, RF unit 640 generates, from the superposedmodulated symbol stream generated by adder 630, a radio-frequency signalas a signal corresponding to the superposed modulated symbol stream tosend such a radio-frequency signal from the antenna.

Stated differently, the superposer constituted by multiplier 614,multiplier 624, and adder 630 superposes the first modulated symbolstream and the second modulated symbol stream at a predeterminedamplitude ratio, thereby generating a multiplexed signal into which thefirst data series and the second data series are multiplexed.Subsequently, RF unit 640 sends the multiplexed signal. Note that themultiplexed signal corresponds to the superposed modulated symbolstream. Also note that the predetermined amplitude ratio may be 1:1, andthat the multiplication may be omitted.

The following shows an example case in which QPSK is used as the firstmapping scheme to describe the operation of converter 625.

For example, when S₁(t) is the t-th modulated symbol in the firstmodulated symbol stream generated by mapper 613, and b₁(t) and b₂(t) area plurality of bits to be mapped onto SAX modulated symbol S₁(t) isgiven by Equation 8.

$\begin{matrix}\left\lbrack {{Math}.\mspace{11mu} 8} \right\rbrack & \; \\{{S_{1}(t)} = \frac{\left( {{2 \cdot {b_{1}(t)}} - 1} \right) + {i \cdot \left( {{2 \cdot {b_{2}(t)}} - 1} \right)}}{\sqrt{2}}} & \left( {{Equation}\mspace{14mu} 8} \right)\end{matrix}$

Here, i denotes the imaginary unit. Modulated symbol S₁(t) may also begiven by an equation in which one of or both of the polarities of thereal part and the imaginary part of Equation 8 are reversed. Bit b₁(t)is a bit that contributes to the real part of modulated symbol SAX Bitb₂(t) is a bit that contributes to the imaginary part of modulatedsymbol SAX

Converter 625 converts, into S′₂(t), the t-th modulated symbol S₂(t) inthe second modulated symbol stream generated by mapper 623, on the basisof modulated symbol S₁(t) as shown by Equation 9.S′ ₂(t)=−sgn(Re[S ₁(t)])·Re[S ₂(t)]−i·sgn(Im[S ₁(t)])·Im[S ₂(t)]  [Math.9]

Here, S′₂(t) is the converted t-th modulated symbol in the secondmodulated symbol stream. Re[S₂(t)] is the value of the real part ofS₂(t), and Im[S₂(t)] is the value of the imaginary part of S₂(t). Also,sgn(Re[S₁(t)]) is the polarity of the real part of S₁(t), andsgn(Im[S₁(t)]) is the polarity of the imaginary part of S₁(t).

Modulated symbol S′₂(t) may be given by an equation in which one of orboth of the polarities of the real part and the imaginary part ofEquation 9 are reversed. Note that the conversion that is based onEquation 9 is substantially the same as the conversion that is based onEquation 7.

As described above, the variation of superposition coding controls thepolarities of the real part and the imaginary part of each secondmodulated symbol in accordance with the first modulated symbol that issuperposed with such a second modulated symbol. Note that the polaritiesof the real part and the imaginary part of each second modulated symbolmay be controlled in accordance with the values of the bits to be mappedonto the first modulated symbol that is superposed with such a secondmodulated symbol. Also, the polarity of one of the real part and theimaginary part of each second modulated symbol may be controlled, or thepolarities of both the real part and the imaginary part of each secondmodulated symbol may be controlled.

FIG. 15 shows an example configuration of transmission device 700 thatmultiplexes two data series onto two layers by the variation ofsuperposition coding, and transmits the multiplexed data series. Theconfiguration of transmission device 700 is different from theconfigurations of transmission devices 500 and 600. The configurationand operation of transmission device 700 will be described withreference to FIG. 15.

Transmission device 700 includes encoder 711, interleaver 712, mapper713, multiplier 714, encoder 721, interleaver 722, mapper 723,multiplier 724, adder 730, and RF unit 740. These structural componentsmay also be implemented as dedicated or general-purpose circuits.Multiplier 714, multiplier 724, and adder 730 can also be representedcollectively as a superposer. RF unit 740 can also be represented as atransmitter. RF unit 740 may include an antenna. Mapper 723 may includea converter.

Encoder 711 encodes an inputted first data series on the basis of afirst error control coding scheme to generate a first bit stream.Interleaver 712 permutes the bits in the first bit stream generated byencoder 711 on the basis of a first permutation rule. Such permutationis also referred to as interleaving.

Mapper 713 maps the first bit stream permuted by interleaver 712 inaccordance with a first mapping scheme to generate a first modulatedsymbol stream that includes a plurality of first modulated symbols. Inthe mapping in accordance with the first mapping scheme, mapper 713 mapseach group of bits that includes a first number of bits in the first bitstream onto one of the signal points in a first constellation inaccordance with the values of such a group of bits.

Encoder 721 encodes an inputted second data series on the basis of asecond error control coding scheme to generate a second bit stream.Interleaver 722 permutes the bits in the second bit stream generated byencoder 721 on the basis of a second permutation rule. Such permutationis also referred to as interleaving.

Mapper 723 converts (modifies) a second mapping scheme in accordancewith the first bit stream to be mapped to the first modulated symbolstream by mapper 713. Mapper 723 then maps the second bit streaminterleaved by interleaver 722 in accordance with the second mappingscheme that has been converted in accordance with the first bit stream.Through these processes, mapper 723 generates a second modulated symbolstream that includes a plurality of second modulated symbols.

In the mapping in accordance with the second mapping scheme, mapper 723maps each group of bits that includes a second number of bits in thesecond bit stream onto one of the signal points in a secondconstellation in accordance with the values of such a group of bits.

Multiplier 714 multiplies each first modulated symbol in the firstmodulated symbol stream by first amplitude coefficient a₁. Multiplier724 multiplies each second modulated symbol in the second modulatedsymbol stream by second amplitude coefficient a₂. Adder 730 superposesfirst modulated symbols multiplied by first amplitude coefficient a₁ andsecond modulated symbols multiplied by second amplitude coefficient a₂to generate a superposed modulated symbol stream that includes aplurality of superposed modulated symbols.

RF unit 740 sends the generated superposed modulated symbol stream as asignal. More specifically, RF unit 740 generates, from the superposedmodulated symbol stream generated by adder 730, a radio-frequency signalas a signal corresponding to the superposed modulated symbol stream tosend such a radio-frequency signal from the antenna.

Stated differently, the superposer constituted by multiplier 714,multiplier 724, and adder 730 superposes the first modulated symbolstream and the second modulated symbol stream at a predeterminedamplitude ratio, thereby generating a multiplexed signal into which thefirst data series and the second data series are multiplexed.Subsequently, RF unit 740 sends the multiplexed signal. Note that themultiplexed signal corresponds to the superposed modulated symbolstream. Also note that the predetermined amplitude ratio may be 1:1, andthat the multiplication may be omitted.

The following shows an example case in which QPSK is used as the firstmapping scheme to describe the operation of mapper 723.

For example, when S₁(t) is the t-th modulated symbol in the firstmodulated symbol stream generated by mapper 713, and b₁(t) and b₂(t) area plurality of bits to be mapped onto S₁(t), modulated symbol S₁(t) isgiven by Equation 10.

$\begin{matrix}\left\lbrack {{Math}.\mspace{11mu} 10} \right\rbrack & \; \\{{S_{1}(t)} = \frac{\left( {{2 \cdot {b_{1}(t)}} - 1} \right) + {i \cdot \left( {{2 \cdot {b_{2}(t)}} - 1} \right)}}{\sqrt{2}}} & \left( {{Equation}\mspace{14mu} 10} \right)\end{matrix}$

Here, i denotes the imaginary unit. Modulated symbol S₁(t) may also begiven by an equation in which one of or both of the polarities of thereal part and the imaginary part of Equation 10 are reversed. Bit b₁(t)is a bit that contributes to the real part of modulated symbol S₁(t).Bit b₂(t) is a bit that contributes to the imaginary part of modulatedsymbol S₁(t).

Mapper 723 performs exclusive-OR between b₁(t) and the bit that mostcontributes to the real part of the second constellation among the bitsin the second bit stream inputted from interleaver 722. Mapper 723 alsoperforms exclusive-OR between b₂(t) and the bit that most contributes tothe imaginary part of the second constellation among the bits in thesecond bit stream inputted from interleaver 722. Mapper 723 then mapsthe second bit stream on which exclusive-OR has been performed, on thebasis of the second constellation.

Here, the bit that most contributes to the real part of the secondconstellation is a bit that causes the polarity of the real part of thesecond constellation to be reversed, for example, when the value of sucha bit is reversed from 0 to 1 or from 1 to 0. Stated differently, thebit that most contributes to the real part of the second constellationrefers to a bit that causes the negative/positive sign of the value ofthe real part of each modulated symbol to be reversed, for example, whenthe value of such a bit is reversed from 0 to 1 or from 1 to 0.

Similarly, the bit that most contributes to the imaginary part of thesecond constellation is a bit that causes the polarity of the imaginarypart of the second constellation to be reversed, for example, when thevalue of such a bit is reversed from 0 to 1 or from 1 to 0. Stateddifferently, the bit that most contributes to the imaginary part of thesecond constellation refers to a bit that causes the negative/positivesign of the value of the imaginary part of each modulated symbol to bereversed when the value of such a bit is reversed from 0 to 1 or from 1to 0.

In the above description, mapper 723 converts the second bit stream,thereby substantially converting the second mapping scheme (the secondconstellation). However, mapper 723 may directly convert the secondmapping scheme (the second constellation) without converting the secondbit stream. Stated differently, mapper 723 may convert thecorrespondence between groups of bits and signal points in the secondconstellation.

Also, the conversion performed by mapper 723 may be performed by theconverter included in mapper 723.

As described above, the variation of superposition coding controls thepolarities of the real part and the imaginary part of each secondmodulated symbol in accordance with the values of the bits to be mappedonto the first modulated symbol that is superposed with such a secondmodulated symbol. Note that the polarities of the real part and theimaginary part of each second modulated symbol may be controlled inaccordance with the first modulated symbol that is superposed with sucha second modulated symbol. Also, the polarity of one of the real partand the imaginary part of each second modulated symbol may becontrolled, or the polarities of both the real part and the imaginarypart of each second modulated symbol may be controlled.

<Sequential Decoding of Signal Obtained by Variation of SuperpositionCoding>

FIG. 16 shows an example configuration of reception device 800 capableof receiving and sequentially decoding the signal on which two dataseries are multiplexed onto two layers by the above-described variationof superposition coding, and capable of obtaining one of or both of themultiplexed two data series. The configuration and operation ofreception device 800 will be described with reference to FIG. 16.

Reception device 800 includes RF unit 830, demapper 811, deinterleaver812, decoder 813, encoder 814, interleaver 815, mapper 816, multiplier817, delayer 818, subtractor 819, converter 820, demapper 821,deinterleaver 822, and decoder 823. These structural components may alsobe implemented as dedicated or general-purpose circuits.

Demapper 811, deinterleaver 812, decoder 813, encoder 814, interleaver815, mapper 816, multiplier 817, delayer 818, subtractor 819, converter820, demapper 821, deinterleaver 822, and decoder 823 can also berepresented collectively as a deriver. RF unit 830 can also berepresented as a receiver. RF unit 830 may include an antenna.

Reception device 800 receives by an antenna the multiplexed signal sentfrom transmission device 500, 600, or 700, and inputs such a multiplexedsignal into RF unit 830. Stated differently, RF unit 830 receives themultiplexed signal via the antenna. The multiplexed signal received byRF unit 830 is also represented as a received signal, and corresponds tothe superposed modulated symbol stream into which the first modulatedsymbol stream and the second modulated symbol stream are multiplexed. RFunit 830 generates a baseband received signal from the radio-frequencyreceived signal.

Demapper 811 demaps the baseband received signal on the basis of thefirst constellation of the first mapping scheme to generate the firstbit likelihood stream. For example, amplitude coefficient a₁ isreflected in the first constellation for demapping.

Deinterleaver 812 permutes the first bit likelihood stream on the basisof a permutation rule that is a reverse rule of the first permutationrule. Such permutation is also referred to as deinterleaving. Decoder813 performs decoding that is based on the first error control codingscheme by use of the first bit likelihood stream permuted bydeinterleaver 812, and outputs the decoding result as the first dataseries.

Here, of the received signal corresponding to the superposed modulatedsymbol stream, demapper 811 treats the components corresponding to thesecond modulated symbols in the second data series as an unknown signal(noise), and performs demapping on the basis of the first constellationof the first mapping scheme.

When only the first data series is to be obtained, reception device 800terminates the process upon completing the estimation of the first dataseries. Meanwhile, when the second data series is to be obtained inaddition to the first data series, or when only the second data seriesis to be obtained, reception device 800 performs the processes describedbelow to obtain the second data series.

Encoder 814 encodes the first data series obtained by decoder 813 on thebasis of the first error control coding scheme to generate the first bitstream. Interleaver 815 permutes the bits in the first bit streamgenerated by encoder 814 on the basis of the first permutation rule.Such permutation is also referred to as interleaving.

Mapper 816 maps the first bit stream permuted by interleaver 815 inaccordance with the first mapping scheme to generate the first modulatedsymbol stream that includes a plurality of first modulated symbols.Multiplier 817 multiplies the first modulated symbol stream outputted bymapper 816 by first amplitude coefficient a₁.

Delayer 818 delays the received signal outputted from RF unit 830 duringthe time from when RF unit 830 outputs the baseband received signal towhen multiplier 817 outputs the reproduced first modulated symbolstream.

Subtractor 819 subtracts, from the received signal delayed by delayer818, the first modulated symbol stream multiplied by first amplitudecoefficient a₁ by multiplier 817. Through this, subtractor 819 removesthe components corresponding to the first modulated symbols from thereceived signal on which the components corresponding to the firstmodulated symbols, the components corresponding to the second modulatedsymbols, and noise are superposed.

Subsequently, subtractor 819 outputs a signal on which the componentscorresponding to the second modulated symbols and noise are superposedas a signal corresponding to the second modulated symbol stream.

Converter 820 converts the signal outputted from subtractor 819 as asignal corresponding to the second modulated symbol stream by use of thefirst bit stream reproduced through encoding, interleaving, etc.Demapper 821 demaps the signal outputted by converter 820 on the basisof the second constellation of the second mapping scheme to generate thesecond bit likelihood stream. For example, amplitude coefficient a₂ isreflected in the second constellation for demapping.

Deinterleaver 822 permutes the second bit likelihood stream on the basisof a permutation rule that is a reverse rule of the second permutationrule. Such permutation is also referred to as deinterleaving. Decoder823 decodes the second bit likelihood stream permuted by deinterleaver822 on the basis of the second error control coding scheme, and outputsthe decoding result as the second data series.

The following shows an example case in which QPSK is used as the firstmapping scheme to describe the operation of converter 820.

For example, when S₁(t) is the t-th modulated symbol in the firstmodulated symbol stream generated by mapper 816, and b₁(t) and b₂(t) area plurality of bits to be mapped onto SAX modulated symbol S₁(t) isgiven by Equation 11.

$\begin{matrix}\left\lbrack {{Math}.\mspace{11mu} 11} \right\rbrack & \; \\{{S_{1}(t)} = \frac{\left( {{2 \cdot {b_{1}(t)}} - 1} \right) + {i \cdot \left( {{2 \cdot {b_{2}(t)}} - 1} \right)}}{\sqrt{2}}} & \left( {{Equation}\mspace{14mu} 11} \right)\end{matrix}$

Here, i denotes the imaginary unit. Modulated symbol S₁(t) may also begiven by an equation in which one of or both of the polarities of thereal part and the imaginary part of Equation 11 are reversed. Bit b₁(t)is a bit that contributes to the real part of modulated symbol SAX Bitb₂(t) is a bit that contributes to the imaginary part of modulatedsymbol SAX

Converter 820 converts, into S′₂(t), signal S₂(t) corresponding to thet-th modulated symbol in the second modulated symbol stream out of thesignal outputted by subtractor 819, on the basis of b₁(t) and b₂(t) asshown by Equation 12.[Math. 12]S′ ₂(t)=(−1)^(b) ¹ ^((t))·Re[S ₂(t)]+i·(−1)^(b) ² ^((t))·Im[S₂(t)]  (Equation 12)

Here, S′₂(t) is the signal that has undergone the conversion. Also,Re[S₂(t)] is the value of the real part of S₂(t), and Im[S₂(t)] is thevalue of the imaginary part of S₂(t). Signal S′₂(t) that has undergonethe conversion may be given by an equation in which one of or both ofthe polarities of the real part and the imaginary part of Equation 12are reversed.

Through the above processes, reception device 800 obtains one of or bothof the first data series and the second data series from the signalreceived by the antenna.

FIG. 17 shows an example configuration of reception device 900 capableof receiving and sequentially decoding the signal on which two dataseries are multiplexed onto two layers by the above-described variationof superposition coding, and capable of obtaining one of or both of themultiplexed two data series. The configuration of reception device 900is different from the configuration of reception device 800. Theconfiguration and operation of reception device 900 will be describedwith reference to FIG. 17.

Reception device 900 includes RF unit 930, demapper 911, deinterleaver912, decoder 913, encoder 914, interleaver 915, mapper 916, multiplier917, delayer 918, subtractor 919, converter 920, demapper 921,deinterleaver 922, and decoder 923. These structural components may alsobe implemented as dedicated or general-purpose circuits.

Demapper 911, deinterleaver 912, decoder 913, encoder 914, interleaver915, mapper 916, multiplier 917, delayer 918, subtractor 919, converter920, demapper 921, deinterleaver 922, and decoder 923 can also berepresented collectively as a deriver. RF unit 930 can also berepresented as a receiver. RF unit 930 may include an antenna.

Reception device 900 receives by an antenna the multiplexed signal sentfrom transmission device 500, 600, or 700, and inputs such a multiplexedsignal into RF unit 930. Stated differently, RF unit 930 receives themultiplexed signal via the antenna. The multiplexed signal received byRF unit 930 is also represented as a received signal, and corresponds tothe superposed modulated symbol stream into which the first modulatedsymbol stream and the second modulated symbol stream are multiplexed. RFunit 930 generates a baseband received signal from the radio-frequencyreceived signal.

Demapper 911 demaps the baseband received signal on the basis of thefirst constellation of the first mapping scheme to generate the firstbit likelihood stream. For example, amplitude coefficient a₁ isreflected in the first constellation for demapping.

Deinterleaver 912 permutes the first bit likelihood stream on the basisof a permutation rule that is a reverse rule of the first permutationrule. Such a permutation is also referred to as deinterleaving. Decoder913 performs decoding that is based on the first error control codingscheme by use of the first bit likelihood stream permuted bydeinterleaver 912, and outputs the decoding result as the first dataseries.

Here, of the received signal corresponding to the superposed modulatedsymbol stream, demapper 911 treats the components corresponding to thesecond modulated symbols in the second data series as an unknown signal(noise), and performs demapping on the basis of the first constellationof the first mapping scheme.

When only the first data series is to be obtained, reception device 900terminates the process upon completing the estimation of the first dataseries. Meanwhile, when the second data series is to be obtained inaddition to the first data series, or when only the second data seriesis to be obtained, reception device 900 performs the processes describedbelow to obtain the second data series.

Encoder 914 encodes the first data series obtained by decoder 913 on thebasis of the first error control coding scheme to generate the first bitstream. Interleaver 915 permutes the bits in the first bit streamgenerated by encoder 914 on the basis of the first permutation rule.Such permutation is also referred to as interleaving.

Mapper 916 maps the first bit stream permuted by interleaver 915 inaccordance with the first mapping scheme to generate the first modulatedsymbol stream that includes a plurality of first modulated symbols.Multiplier 917 multiplies the first modulated symbol stream outputted bymapper 916 by first amplitude coefficient a₁.

Delayer 918 delays the received signal outputted from RF unit 930 duringthe time from when RF unit 930 outputs the baseband received signal towhen multiplier 917 outputs the reproduced first modulated symbolstream. Subtractor 919 subtracts, from the received signal delayed bydelayer 918, the first modulated symbol stream multiplied by firstamplitude coefficient a₁ by multiplier 917. Through this, subtractor 919removes the components corresponding to the first modulated symbols fromthe received signal on which the components corresponding to the firstmodulated symbols, the components corresponding to the second modulatedsymbols, and noise are superposed. Subsequently, subtractor 919 outputsa signal on which the components corresponding to the second modulatedsymbols and noise are superposed as a signal corresponding to the secondmodulated symbol stream.

Converter 920 converts the signal outputted from subtractor 919 as asignal corresponding to the second modulated symbol stream by use of thefirst modulated symbol stream reproduced through encoding, interleaving,mapping, etc. Demapper 921 demaps the signal outputted by converter 920on the basis of the second constellation of the second mapping scheme togenerate the second bit likelihood stream. For example, amplitudecoefficient a₂ is reflected in the second constellation for demapping.

Deinterleaver 922 permutes the second bit likelihood stream on the basisof a permutation rule that is a reverse rule of the second permutationrule. Such permutation is also referred to as deinterleaving. Decoder923 decodes the second bit likelihood stream permuted by deinterleaver922 on the basis of the second error control coding scheme, and outputsthe decoding result as the second data series.

The following shows an example case in which QPSK is used as the firstmapping scheme to describe the operation of converter 920.

For example, when S₁(t) is the t-th modulated symbol in the firstmodulated symbol stream generated by mapper 916, and b₁(t) and b₂(t) area plurality of bits to be mapped onto SAX modulated symbol S₁(t) isgiven by Equation 13.

$\begin{matrix}\left\lbrack {{Math}.\mspace{11mu} 13} \right\rbrack & \; \\{{S_{1}(t)} = \frac{\left( {{2 \cdot {b_{1}(t)}} - 1} \right) + {i \cdot \left( {{2 \cdot {b_{2}(t)}} - 1} \right)}}{\sqrt{2}}} & \left( {{Equation}\mspace{14mu} 13} \right)\end{matrix}$

Here, i denotes the imaginary unit. Modulated symbol S₁(t) may also begiven by an equation in which one of or both of the polarities of thereal part and the imaginary part of Equation 13 are reversed. Bit b₁(t)is a bit that contributes to the real part of modulated symbol S₁(t).Bit b₂(t) is a bit that contributes to the imaginary part of modulatedsymbol SAX

Converter 920 converts, into S′₂(t), signal S₂(t) corresponding to thet-th modulated symbol in the second modulated symbol stream out of thesignal outputted by subtractor 919, on the basis of modulated symbolS₁(t) as shown by Equation 14.[Math. 14]S′ ₂(t)=−sgn(Re[S ₁(t)])·Re[S ₂(t)]−i·sgn(Im[S ₁(t)])·Im[S ₂(t)]

Here, S′₂(t) is the signal that has undergone the conversion. Also,Re[S₂(t)] is the value of the real part of S₂(t), and Im[S₂(t)] is thevalue of the imaginary part of S₂(t). Also, sgn(Re[S₁(t)]) is thepolarity of the real part of S₁(t), and sgn(Im[S₁(t)]) is the polarityof the imaginary part of S₁(t). Signal S′₂(t) that has undergone theconversion may be given by an equation in which one of or both of thepolarities of the real part and the imaginary part of Equation 14 arereversed. Note that the conversion that is based on Equation 14 issubstantially the same as the conversion that is based on Equation 12.

Through the above processes, reception device 900 obtains one of or bothof the first data series and the second data series from the signalreceived by the antenna.

FIG. 18 shows an example configuration of reception device 1000 capableof receiving and sequentially decoding the signal on which two dataseries are multiplexed onto two layers by the above-described variationof superposition coding, and capable of obtaining one of or both of themultiplexed two data series. The configuration of reception device 1000is different from the configurations of reception devices 800 and 900.The configuration and operation of reception device 1000 will bedescribed with reference to FIG. 18.

Reception device 1000 includes RF unit 1030, demapper 1011,deinterleaver 1012, decoder 1013, encoder 1014, interleaver 1015, mapper1016, multiplier 1017, delayer 1018, subtractor 1019, demapper 1021,deinterleaver 1022, and decoder 1023. These structural components mayalso be implemented as dedicated or general-purpose circuits.

Demapper 1011, deinterleaver 1012, decoder 1013, encoder 1014,interleaver 1015, mapper 1016, multiplier 1017, delayer 1018, subtractor1019, demapper 1021, deinterleaver 1022, and decoder 1023 can also berepresented collectively as a deriver. RF unit 1030 can also berepresented as a receiver. RF unit 1030 may include an antenna. Demapper1021 may include a converter.

Reception device 1000 receives by an antenna the multiplexed signal sentfrom transmission device 500, 600, or 700, and inputs such a multiplexedsignal into RF unit 1030. Stated differently, RF unit 1030 receives themultiplexed signal via the antenna. The multiplexed signal received byRF unit 1030 is also represented as a received signal, and correspondsto the superposed modulated symbol stream into which the first modulatedsymbol stream and the second modulated symbol stream are multiplexed. RFunit 1030 generates a baseband received signal from the radio-frequencyreceived signal.

Demapper 1011 demaps the baseband received signal on the basis of thefirst constellation of the first mapping scheme to generate the firstbit likelihood stream. For example, amplitude coefficient a₁ isreflected in the first constellation for demapping.

Deinterleaver 1012 permutes the first bit likelihood stream on the basisof a permutation rule that is a reverse rule of the first permutationrule. Such permutation is also referred to as deinterleaving. Decoder1013 performs decoding that is based on the first error control codingscheme by use of the first bit likelihood stream permuted bydeinterleaver 1012, and outputs the decoding result as the first dataseries.

Here, of the received signal corresponding to the superposed modulatedsymbol stream, demapper 1011 treats the components corresponding to thesecond modulated symbols in the second data series as an unknown signal(noise), and performs demapping on the basis of the first constellationof the first mapping scheme.

When only the first data series is to be obtained, reception device 1000terminates the process upon completing the estimation of the first dataseries. Meanwhile, when the second data series is to be obtained inaddition to the first data series, or when only the second data seriesis to be obtained, reception device 1000 performs the processesdescribed below to obtain the second data series.

Encoder 1014 encodes the first data series obtained by decoder 1013 onthe basis of the first error control coding scheme to generate the firstbit stream. Interleaver 1015 permutes the bits in the first bit streamgenerated by encoder 1014 on the basis of the first permutation rule.Such permutation is also referred to as interleaving.

Mapper 1016 maps the first bit stream permuted by interleaver 1015 inaccordance with the first mapping scheme to generate the first modulatedsymbol stream that includes a plurality of first modulated symbols.Multiplier 1017 multiplies the first modulated symbol stream outputtedby mapper 1016 by first amplitude coefficient a₁.

Delayer 1018 delays the received signal outputted from RF unit 1030during the time from when RF unit 1030 outputs the baseband receivedsignal to when multiplier 1017 outputs the reproduced first modulatedsymbol stream.

Subtractor 1019 subtracts, from the received signal delayed by delayer1018, the first modulated symbol stream multiplied by first amplitudecoefficient a₁ by multiplier 1017. Through this, subtractor 1019 removesthe components corresponding to the first modulated symbols from thereceived signal on which the components corresponding to the firstmodulated symbols, the components corresponding to the second modulatedsymbols, and noise are superposed. Subsequently, subtractor 1019 outputsa signal on which the components corresponding to the second modulatedsymbols and noise are superposed as a signal corresponding to the secondmodulated symbol stream.

Demapper 1021 demaps the signal outputted from subtractor 1019 as asignal corresponding to the second modulated symbol stream on the basisof the second constellation of the second mapping scheme to generate thesecond bit likelihood stream. Such a process reflects the first bitstream reproduced through encoding, interleaving, etc. For example,amplitude coefficient a₂ is reflected in the second constellation fordemapping.

Deinterleaver 1022 permutes the second bit likelihood stream on thebasis of a permutation rule that is a reverse rule of the secondpermutation rule. Such permutation is also referred to asdeinterleaving. Decoder 1023 decodes the second bit likelihood streampermuted by deinterleaver 1022 on the basis of the second error controlcoding scheme, and outputs the decoding result as the second dataseries.

The following shows an example case in which QPSK is used as the firstmapping scheme to describe the operation of demapper 1021.

For example, when S₁(t) is the t-th modulated symbol in the firstmodulated symbol stream generated by mapper 1016, and b₁(t) and b₂(t)are a plurality of bits to be mapped onto SAX modulated symbol S₁(t) isgiven by Equation 15.

$\begin{matrix}\left\lbrack {{Math}.\mspace{11mu} 15} \right\rbrack & \; \\{{S_{1}(t)} = \frac{\left( {{2 \cdot {b_{1}(t)}} - 1} \right) + {i \cdot \left( {{2 \cdot {b_{2}(t)}} - 1} \right)}}{\sqrt{2}}} & \left( {{Equation}\mspace{14mu} 15} \right)\end{matrix}$

Here, i denotes the imaginary unit. Modulated symbol S₁(t) may also begiven by an equation in which one of or both of the polarities of thereal part and the imaginary part of Equation 15 are reversed. Bit b₁(t)is a bit that contributes to the real part of modulated symbol S₁(t).Bit b₂(t) is a bit that contributes to the imaginary part of modulatedsymbol S₁(t).

Demapper 1021 demaps signal S₂(t) outputted from subtractor 1019 as asignal corresponding to the t-th modulated symbol in the secondmodulated symbol stream on the basis of the second constellation of thesecond mapping scheme.

Demapper 1021 reverses the bit likelihood corresponding to the bit thatmost contributes to the real part of the second constellation inaccordance with b₁(t) among the bit likelihoods in the bit likelihoodstream obtained by demapping. Demapper 1021 also reverses the bitlikelihood corresponding to the bit that most contributes to theimaginary part of the second constellation in accordance with b₂(t)among the bit likelihoods in the bit likelihood stream obtained bydemapping.

For example, demapper 1021 performs exclusive-OR between b₁(t) and thebit likelihood corresponding to the bit that most contributes to thereal part of the second constellation among the bit likelihoods in thebit likelihood stream obtained by demapping. Demapper 1021 also performsexclusive-OR between b₂(t) and the bit likelihood corresponding to thebit that most contributes to the imaginary part of the secondconstellation among the bit likelihoods in the bit likelihood streamobtained by demapping.

Demapper 1021 then outputs the bit likelihood stream that has undergonethe above-described reversal processes as the second bit likelihoodstream.

In the above description, demapper 1021 converts the bit likelihoodstream, thereby substantially converting the second mapping scheme (thesecond constellation). However, demapper 1021 may directly convert thesecond mapping scheme (the second constellation) without converting thebit likelihood stream. Stated differently, demapper 1021 may convert thecorrespondence between groups of bits and signal points in the secondconstellation.

Also, the conversion performed by demapper 1021 may be performed by theconverter included in demapper 1021.

Through the above processes, reception device 1000 obtains one of orboth of the first data series and the second data series from the signalreceived by the antenna.

<Parallel Decoding of Signal Obtained by Variation of SuperpositionCoding>

The following describes a reception method for parallel decoding of asignal obtained by the variation of superposition coding according tothe present embodiment. The configuration of the transmission device isthe same as the configuration of transmission device 500 shown in FIG.13, transmission device 600 shown in FIG. 14, or transmission device 700shown in FIG. 15, and thus will not be described. In parallel decodingin the variation of superposition coding, the reception device treatsthe components of the modulated symbol stream in the first layer as anunknown signal (noise) to decode the second layer, without removing thecomponents of the modulated symbol stream in the first layer included inthe received signal.

FIG. 19 shows an example configuration of reception device 1100 capableof receiving and performing parallel decoding on the signal on which twodata series are multiplexed onto two layers by the variation ofsuperposition coding, and capable of obtaining one of or both of themultiplexed two data series. The configuration and operation ofreception device 1100 will be described with reference to FIG. 19.

Reception device 1100 includes RF unit 1130, demapper 1110,deinterleaver 1112, decoder 1113, deinterleaver 1122, and decoder 1123.These structural components may also be implemented as dedicated orgeneral-purpose circuits. Demapper 1110, deinterleaver 1112, decoder1113, deinterleaver 1122, and decoder 1123 can also be representedcollectively as a deriver. RF unit 1130 can also be represented as areceiver. RF unit 1130 may include an antenna.

Reception device 1100 receives by an antenna the multiplexed signal sentfrom transmission device 500, 600, or 700, and inputs such a multiplexedsignal into RF unit 1130. Stated differently, RF unit 1130 receives themultiplexed signal via the antenna. The multiplexed signal received byRF unit 1130 is also represented as a received signal. RF unit 1130generates a baseband received signal from the radio-frequency receivedsignal.

Demapper 1110 demaps the baseband received signal to generate the firstbit likelihood stream and the second bit likelihood stream. For example,demapper 1110 performs demapping on the basis of a variationsuperposition constellation that shows the arrangement of signal pointsof superposed modulated symbols obtained by superposing the firstmodulated symbols and the second modulated symbols by the variation ofsuperposition coding.

The variation superposition constellation is determined in accordancewith the first constellation of the first mapping scheme, the secondconstellation of the second mapping scheme, first amplitude coefficienta₁, first amplitude coefficient a₂, etc.

FIG. 20 shows the variation superposition constellation that supportsthe variation of superposition coding. More specifically, the variationsuperposition constellation is a combination of the QPSK constellationshown in FIG. 4 and the Nu-256QAM constellation shown in FIG. 5.

Even more specifically, the Nu-256QAM constellation (256 signal points)is placed on each of the four regions in the complex plane in accordancewith the four signal points of the QPSK constellation. These fourregions, each corresponding to Nu-256QAM constellation, may partiallyoverlap with each other. The present variation superpositionconstellation reflects the conversion performed on the second modulatedsymbol stream.

For example, when the Nu-256QAM constellation is combined with a signalpoint with a positive real part among the four signal points of the QPSKconstellation, the polarity of the real part of the Nu-256QAMconstellation is reversed. Also, for example, when the Nu-256QAMconstellation is combined with a signal point with a positive imaginarypart among the four signal points of the QPSK constellation, thepolarity of the imaginary part of the Nu-256QAM constellation isreversed.

More specifically, a first signal point, a second signal point, a thirdsignal point, a fourth signal point, a fifth signal point, and a sixthsignal point are shown in FIG. 20. When the polarity of the real part ofthe Nu-256QAM constellation is not reversed, the first signal point andthe third signal point correspond to the same bit values of the secondbit stream. Similarly, when the polarity of the imaginary part of theNu-256QAM constellation is not reversed, the fourth signal point and thesixth signal point correspond to the same bit values of the second bitstream.

When the polarity of the real part of the Nu-256QAM constellation isreversed, the first signal point and the second signal point correspondto the same bit values of the second bit stream. Also, when the polarityof the imaginary part of the Nu-256QAM constellation is reversed, thefourth signal point and the fifth signal point correspond to the samebit values of the second bit stream. Stated differently, such reversalenables a plurality of signal points that correspond to the same bitvalues of the second bit stream to approach each other and converge.This mitigates the effect of noise on demapping.

Demapper 1110 performs demapping on the basis of the variationsuperposition constellation as shown in FIG. 20. Stated differently,demapper 1110 generates the first bit likelihood stream with themodulated symbol stream of the second layer remaining unknown, andgenerates the second bit likelihood stream with the modulated symbolstream of the first layer remaining unknown. Note that demapper 1110 mayuse the first constellation of the first mapping scheme to generate thefirst bit likelihood stream, and may use the above-described variationsuperposition constellation to generate the second bit likelihoodstream.

The first constellation, when used to generate the first bit likelihoodstream, enables demapper 1110 to reduce the number of signal points thatshould be considered in generating the first bit likelihood stream,compared to when the variation superposition constellation is also usedto generate the first bit likelihood stream. This thus enables demapper1110 to reduce the number of arithmetic computations.

Demapper 1110 corresponds, for example, to the first demapper thatdemaps the received signal to generate the first bit likelihood streamand the second demapper that demaps the received signal to generate thesecond bit likelihood stream. Demapper 1110 may include the firstdemapper that demaps the received signal to generate the first bitlikelihood stream and the second demapper that demaps the receivedsignal to generate the second bit likelihood stream.

Demapper 1110 may convert the second bit likelihood stream that isgenerated using not the variation superposition constellation but thesuperposition constellation, in accordance with the first bit likelihoodstream. This enables demapper 1110 to obtain the same second bitlikelihood stream as the second bit likelihood stream that is generatedusing the variation superposition constellation.

Demapper 1110 may convert the multiplexed signal without using thevariation superposition constellation to obtain the same second bitlikelihood stream as the second bit likelihood stream that is generatedusing the variation superposition constellation.

Deinterleaver 1112 permutes the first bit likelihood stream on the basisof a permutation rule that is a reverse rule of the first permutationrule. Such permutation is also referred to as deinterleaving. Decoder1113 decodes the first bit likelihood stream permuted by deinterleaver1112 on the basis of the first error control coding scheme, and outputsthe decoding result as the first data series.

Deinterleaver 1122 permutes the second bit likelihood stream on thebasis of a permutation rule that is a reverse rule of the secondpermutation rule. Such permutation is also referred to asdeinterleaving. Decoder 1123 decodes the second bit likelihood streampermuted by deinterleaver 1122 on the basis of the second error controlcoding scheme, and outputs the decoding result as the second dataseries.

Through the above processes, reception device 1100 obtains one of orboth of the first data series and the second data series from the signalreceived by the antenna.

Note that transmission devices 500, 600, and 700, and reception devices800, 900, 1000, and 1100 may omit permutation (interleaving anddeinterleaving) as in the case of Embodiment 1. Stated differently,their respective interleavers and deinterleavers are optional structuralcomponents, and thus may not be included in these devices.

Interleaving and deinterleaving, however, make a pair. As such, whentransmission devices 500, 600, and 700 include their respectiveinterleavers, reception devices 800, 900, 1000, and 1100 basicallyinclude their respective deinterleavers and interleavers. Meanwhile,when transmission devices 500, 600, and 700 do not include theirrespective interleavers, reception devices 800, 900, 1000, and 1100 donot include their respective deinterleavers and interleavers.

Amplitude coefficient a₁ may be reflected in the mapping for generatingthe first modulated symbols performed in reception devices 800, 900, and1000. In such a case, the multiplication of amplitude coefficient a₁ maybe omitted. Reception devices 800, 900, and 1000 thus may not includemultipliers 817, 917, and 1017, respectively.

Error control coding on the first data series and the second data seriesmay be performed by an external device. In such a case, transmissiondevices 500, 600, and 700 may omit error control coding, and may notinclude encoders 511, 521, 611, 621, 711, and 721.

FIG. 21 is a flowchart of example operations performed by transmissiondevice 500. First, mapper 513 maps the first bit stream of the firstdata series to generate the first modulated symbol stream of the firstdata series (S301). Then, mapper 523 maps the second bit stream of thesecond data series to generate the second modulated symbol stream of thesecond data series (S302).

Converter 525 subjects the second modulated symbol stream to conversionin accordance with the first modulation symbol stream (S303). Morespecifically, converter 525 converts the second modulated symbol streamin accordance with the first bit stream, thereby subjecting the secondmodulated symbol stream to conversion in accordance with the firstmodulated symbol stream.

Next, the superposer constituted by first multiplier 514, secondmultiplier 524, and adder 530 superposes the first modulated symbolstream and the second modulated symbol stream that has been subjected toconversion in accordance with the first modulated symbol stream at apredetermined amplitude ratio, thereby generating the multiplexed signal(S304). RF unit 540 then sends the generated multiplexed signal (S305).

Note that in the above operation example, transmission device 500converts the second modulated symbol stream in accordance with the firstbit stream, thereby subjecting the second modulated symbol stream toconversion in accordance with the first modulated symbol stream (S303).Alternatively, transmission device 500 may convert the second modulatedsymbol stream in accordance with the first modulated symbol stream, asin the case of transmission device 600, thereby subjecting the secondmodulated symbol stream to conversion in accordance with the firstmodulated symbol stream.

Alternatively, as in the case of transmission device 700, transmissiondevice 500 may convert the second bit stream or the second mappingscheme (the second constellation) used to generate the second modulatedsymbol stream, in accordance with the first bit stream. Through this,the second modulated symbol stream may be subjected to conversion inaccordance with the first modulated symbol stream. In such a case, thesecond bit stream or the second mapping scheme is converted before thesecond modulated symbol stream is generated.

Stated differently, the second bit stream, the second mapping scheme, orthe second modulated symbol stream may be converted in accordance withthe first bit stream or the first modulated symbol stream, therebysubjecting the second modulated symbol stream to conversion inaccordance with the first modulated symbol stream.

Converter 525 may subject the second modulated symbol stream toconversion in accordance with the first modulated symbol stream, therebycontrolling the polarities of the real part and the imaginary part ofeach modulated symbol in the second modulated symbol stream. Throughthis, converter 525 may reverse the polarity of the real part of eachsecond modulated symbol when the real part of the corresponding firstmodulated symbol satisfies a predetermined real part condition, and mayreverse the polarity of the imaginary part of each second modulatedsymbol when the imaginary part of the corresponding first modulatedsymbol satisfies a predetermined condition.

The predetermined real part condition may be a condition that thepolarity of the real part should be a predetermined polarity of the realpart, or may be a condition that the real part should be within apredetermined range of the real part greater than or equal to one. Thepredetermined range of the real part greater than or equal to one may bea positive range or a negative range. Similarly, the predeterminedimaginary part condition may be a condition that the polarity of theimaginary part should be a predetermined polarity of the imaginary part,or may be a condition that the imaginary part should be within apredetermined range of the imaginary part greater than or equal to one.The predetermined range of the imaginary part greater than or equal toone may be a positive range or a negative range.

FIG. 22 is a flowchart of example operations performed by receptiondevices 800, 900, 1000, and 1100. First, the receiver receives themultiplexed signal (S401). Here, the receiver is RF unit 830 ofreception device 800, RF unit 930 of reception device 900, RF unit 1030of reception device 1000, or RF unit 1130 of reception device 1100.

The multiplexed signal is a signal into which a plurality of data seriesincluding the first data series in the first layer and the second dataseries in the second layer are multiplexed. The multiplexed signal isalso a signal on which the first modulated symbol stream and the secondmodulated symbol stream are superposed at a predetermined amplituderatio.

The first modulated symbol stream is a modulated symbol stream that isgenerated by mapping the first bit stream of the first data series. Thesecond modulated symbol stream is a modulated symbol stream that isgenerated by mapping the second bit stream of the second data series,and that has been subjected to conversion in accordance with the firstmodulated symbol stream.

Next, the deriver derives at least one of the first data series or thesecond data series from the multiplexed signal (S402).

The deriver of reception device 800 is constituted, for example, bydemapper 811, deinterleaver 812, decoder 813, encoder 814, interleaver815, mapper 816, multiplier 817, delayer 818, subtractor 819, converter820, demapper 821, deinterleaver 822, and decoder 823.

The deriver of reception device 900 is constituted, for example, bydemapper 911, deinterleaver 912, decoder 913, encoder 914, interleaver915, mapper 916, multiplier 917, delayer 918, subtractor 919, converter920, demapper 921, deinterleaver 922, and decoder 923

The deriver of reception device 1000 is constituted, for example, bydemapper 1011, deinterleaver 1012, decoder 1013, encoder 1014,interleaver 1015, mapper 1016, multiplier 1017, delayer 1018, subtractor1019, demapper 1021, deinterleaver 1022, and decoder 1023

The deriver of reception device 1100 is constituted, for example, bydemapper 1110, deinterleaver 1112, decoder 1113, deinterleaver 1122, anddecoder 1123.

In accordance with the above operations, the multiplexed signal isreceived into which the first modulated symbol stream and the secondmodulated symbol stream that has been subjected to conversion inaccordance with the first modulated symbol stream are multiplexed. Then,at least one of the first data series or the second data series isderived from such a multiplexed signal. Stated differently, such aconfiguration enables: the reception of the multiplexed signal that hasbeen superposed in such a manner that reduces performance degradation atthe time of parallel decoding: and an efficient derivation of one of orboth of the first data series and the second data series from such amultiplexed signal.

Reception device 1100 as shown in FIG. 19 that performs paralleldecoding has lower performance in decoding the second layer than that ofreception devices 800, 900, and 1000 as shown in FIG. 16, FIG. 17, andFIG. 18 that perform sequential decoding.

FIG. 23 shows an example simulation result of the transmission capacityof the second layer when the ratio between signal power P_(s1) of thefirst layer and signal power P_(s2) of the second layer is P_(s1):P_(s2)=2:1. In FIG. 23, the lateral axis represents as dB (decibel) theratio of signal power P_(s) to noise power P_(n) (SNR), and the verticalaxis represents transmission capacity. In FIG. 23, the solid lineindicates the transmission capacity of the second layer when sequentialdecoding is performed, and the broken line indicates the transmissioncapacity of the second layer when parallel decoding is performed.

As FIG. 23 shows, in the decoding of the second layer, parallel decodinginvolves an increased SNR with respect to the same transmission capacityand a decreased transmission capacity with respect to the same SNR,compared to sequential decoding.

As described above, reception device 1100 according to the presentembodiment that performs parallel decoding has lower performance indecoding the second data series transmitted on the second layer thanthat of reception devices 800, 900, and 1000 that perform sequentialdecoding. However, reception device 1100 reduces the number ofstructural components required to decode the second layer.

More specifically, reception device 1100 eliminates the need for thestructural components that are required by reception devices 800, 900,and 1000 shown in FIG. 16, FIG. 17, and FIG. 18 performing sequentialdecoding to reproduce the modulated symbol stream of the first layer.Stated differently, encoders 814, 914, and 1014, interleavers 815, 915,and 1015, mappers 816, 916, and 1016, and multipliers 817, 917, and 1017are not required.

Reception device 1100 also eliminates the need for delayers 818, 918,and 1018 that delay the received signal, and subtractors 819, 919, and1019 that remove the components of the modulated symbols in the firstlayer reproduced from the received signal.

The circuit size can be thus reduced. Reception device 1100 alsorequires a smaller number of arithmetic computations and lower powerconsumption than those required by reception devices 800, 900, and 1000.

Reception devices 800, 900, and 1000 shown in FIG. 16, FIG. 17, and FIG.18 that perform sequential decoding demodulate the first layer in thereceived signal to obtain the first data series, and generate the firstmodulated symbol stream from the obtained first data series.Subsequently, reception devices 800, 900, and 1000 start demodulatingthe second layer in the received signal to obtain the second dataseries.

Meanwhile, reception device 1100 according to the present embodimentthat performs parallel decoding is capable of simultaneously obtainingthe first data series and the second data series in parallel, therebyreducing processing delays.

The reception device may observe the SNR of the received signal to makeselection between parallel decoding to be performed when the SNR is highand sequential decoding to be performed when the SNR is low.

In such a case, reception device 800 shown in FIG. 16 includes, forexample, a controller that makes selection between sequential decodingand parallel decoding depending on the SNR. Such a controller may beincluded in RF unit 830 or demapper 821. Furthermore, demapper 821 isconfigured to perform demapping based on the variation superpositionconstellation, which is described as an operation performed by demapper1110 shown in FIG. 19, in addition to demapping that is based on thesecond constellation.

Demapper 821 switches between demapping to be performed on the signaloutputted from converter 820 on the basis of the second constellationand demapping to be performed on the signal outputted from RF unit 830on the basis of the variation superposition constellation. For example,demapper 821 switches between these demapping operations in accordancewith a control signal from the controller.

Note that such a configuration is also obtained by a combination ofreception device 400 shown in FIG. 11, reception device 800 (converter820, demapper 821, etc.) shown in FIG. 16, and reception device 1100(demapper 1110, etc.) shown in FIG. 19.

Another configuration is that reception device 900 shown in FIG. 17includes, for example, a controller that makes selection betweensequential decoding and parallel decoding depending on the SNR. Such acontroller may be included in RF unit 930 or demapper 921. Furthermore,demapper 921 is configured to perform demapping based on the variationsuperposition constellation, which is described as an operationperformed by demapper 1110 shown in FIG. 19, in addition to demappingthat is based on the first bit stream and the second constellation.

Demapper 921 switches between demapping to be performed on the signaloutputted from converter 920 on the basis of the second constellationand demapping to be performed on the signal outputted from RF unit 930on the basis of the variation superposition constellation. For example,demapper 921 switches between these demapping operations in accordancewith a control signal from the controller.

Note that such a configuration is also obtained by a combination ofreception device 400 shown in FIG. 11, reception device 900 (converter920, demapper 921, etc.) shown in FIG. 17, and reception device 1100(demapper 1110, etc.) shown in FIG. 19.

Still another configuration is that reception device 1000 shown in FIG.18 includes, for example, a controller that makes selection betweensequential decoding and parallel decoding depending on the SNR. Such acontroller may be included in RF unit 1030 or demapper 1021.Furthermore, demapper 1021 is configured to perform demapping based onthe variation superposition constellation, which is described as anoperation performed by demapper 1110 shown in FIG. 19, in addition todemapping that is based on the first bit stream and the secondconstellation.

Demapper 1021 switches between demapping to be performed on the signaloutputted from subtractor 1019 on the basis of the second constellationand demapping to be performed on the signal outputted from RF unit 1030on the basis of the variation superposition constellation. For example,demapper 1021 switches between these demapping operations in accordancewith a control signal from the controller.

Note that such a configuration is also obtained by a combination ofreception device 400 shown in FIG. 11, reception device 1000 (demapper1021, etc.) shown in FIG. 18, and reception device 1100 (demapper 1110,etc.) shown in FIG. 19.

As described above, reception devices 800, 900, and 1000 performparallel decoding when the SNR is high, thereby reducing the number ofarithmetic computations and power consumption. Reception devices 800,900, and 1000 also perform parallel decoding when the SNR is high,thereby reducing processing delays. Meanwhile, reception devices 800,900, and 1000 perform sequential decoding when the SNR is low, therebyincreasing the possibility of correctly decoding the second data series.

Comparison between the transmission capacity in the multiplexing schemeutilizing superposition coding shown in FIG. 10 and the transmissioncapacity in the multiplexing scheme utilizing the variation ofsuperposition coding shown in FIG. 23 presents the findings describedbelow.

The characteristics of the transmission capacities exhibited bysequential decoding (indicated by the solid line) are the same betweenthe multiplexing scheme utilizing superposition coding (FIG. 10) and themultiplexing scheme utilizing the variation of superposition coding(FIG. 23). Meanwhile, the characteristics of the transmission capacitiesexhibited by parallel decoding (indicated by the broken line) areimproved by use of the multiplexing scheme utilizing the variation ofsuperposition coding (FIG. 23) compared to the multiplexing schemeutilizing the superposition coding (FIG. 10). Stated differently, themultiplexing scheme utilizing the variation of superposition codingprovides desirable results both in sequential decoding and paralleldecoding.

Embodiment 4

<Variation of Superposition Coding (Modified Superposition Coding)>

The present embodiment describes a method of multiplexing a plurality ofdata series using a variation of superposition coding (modifiedsuperposition coding), which is a modified version of theabove-described superposition coding, and transmitting the plurality ofmultiplexed data series.

FIG. 24 shows an example configuration of transmission device 1200 thatmultiplexes two data series onto two layers using the variation ofsuperposition coding, and transmits a multiplexed data series. Theconfiguration and operation of transmission device 1200 is to bedescribed with reference to FIG. 24.

Transmission device 1200 includes encoder 1211, interleaver 1212, mapper1213, multiplier 1214, encoder 1221, interleaver 1222, mapper 1223,converter 1225, multiplier 1224, adder 1230, and RF unit 1240. Thesestructural components may also be implemented as dedicated orgeneral-purpose circuits. Multiplier 1214, multiplier 1224, and adder1230 can also be represented collectively as a superposer. RF unit 1240can also be represented as a transmitter. RF unit 1240 may include anantenna.

Encoder 1211 encodes an inputted first data series on the basis of afirst error control coding scheme to generate a first bit stream.Interleaver 1212 permutes the bits in the first bit stream generated byencoder 1211 on the basis of a first permutation rule. Such permutationis also referred to as interleaving.

Mapper 1213 maps the first bit stream permuted by interleaver 1212 inaccordance with a first mapping scheme to generate a first modulatedsymbol stream that includes a plurality of first modulated symbols. Inthe mapping in accordance with the first mapping scheme, mapper 1213maps each group of bits that includes a first number of bits in thefirst bit stream onto one of the signal points in a first constellationin accordance with the values of such a group of bits.

When PSK modulation such as BPSK and QPSK, or QAM modulation such as16QAM and 64QAM is used as the first mapping scheme, each firstmodulated symbol can be represented by a complex number, for example,with the real part representing the magnitude of the in-phase componentand the imaginary part representing the magnitude of the orthogonalcomponent. Meanwhile, when PAM modulation is used as the first mappingscheme, each first modulated symbol can be represented by a real number.

Encoder 1221 encodes an inputted second data series on the basis of asecond error control coding scheme to generate a second bit stream.Interleaver 1222 permutes the bits in the second bit stream generated byencoder 1221 on the basis of a second permutation rule. Such permutationis also referred to as interleaving.

Mapper 1223 maps the second bit stream permuted by interleaver 1222 inaccordance with a second mapping scheme to generate a second modulatedsymbol stream that includes a plurality of second modulated symbols. Inthe mapping in accordance with the second mapping scheme, mapper 1223maps each group of bits that includes a second number of bits in thesecond bit stream onto one of the signal points in a secondconstellation in accordance with the values of such a group of bits.

When PSK modulation such as BPSK and QPSK, or QAM modulation such as16QAM and 64QAM is used as the second mapping scheme, each secondmodulated symbol can be represented by a complex number, for example,with the real part representing the magnitude of the in-phase componentand the imaginary part representing the magnitude of the orthogonalcomponent. Meanwhile, when PAM modulation is used as the second mappingscheme, each second modulated symbol can be represented by a realnumber. Any one of a uniform constellation and a non-uniformconstellation may be used as the second mapping scheme.

Converter 1225 converts each second modulated symbol to be superposedwith the corresponding first modulated symbol, on the basis of thevalues of the bits used to generate such a first modulated symbol.Through this, converter 1225 converts the second modulated symbolstream.

Multiplier 1214 multiplies each first modulated symbol in the firstmodulated symbol stream by first amplitude coefficient a₁. Multiplier1224 multiplies, by second amplitude coefficient a₂, each secondmodulated symbol in the second modulated symbol stream converted byconverter 1225.

Multiplier 1224 may multiply both the real part and the imaginary partof each second modulated symbol by second amplitude coefficient a₂, ormay multiply only one of the real part and the imaginary part by secondamplitude coefficient a₂. Alternatively, multiplier 1224 may multiplythe real part and the imaginary part of each second modulated symbol bydifferent amplitude coefficients.

For example, when a first modulated symbol is constituted by only a realpart, multiplier 1224 may multiply only the real part of a secondmodulated symbol by second amplitude coefficient a₂. Multiplier 1224does not need to multiply the imaginary part of the second modulatedsymbol by an amplitude coefficient, or may multiply the imaginary partby an amplitude coefficient smaller than second amplitude coefficienta₂.

Adder 1230 superposes first modulated symbols multiplied by firstamplitude coefficient a₁ and second modulated symbols multiplied bysecond amplitude coefficient a₂ to generate a superposed modulatedsymbol stream that includes a plurality of superposed modulated symbols.

RF unit 1240 sends the generated superposed modulated symbol stream as asignal. More specifically, RF unit 1240 generates, from the superposedmodulated symbol stream generated by adder 1230, a radio-frequencysignal as a signal corresponding to the superposed modulated symbolstream to send such a radio-frequency signal from the antenna.

Stated differently, the superposer constituted by multiplier 1214,multiplier 1224, and adder 1230 superposes the first modulated symbolstream and the second modulated symbol stream at a predeterminedamplitude ratio, thereby generating a multiplexed signal into which thefirst data series and the second data series are multiplexed.Subsequently, RF unit 1240 sends the multiplexed signal. Note that themultiplexed signal corresponds to the superposed modulated symbolstream.

Also the predetermined amplitude ratio may be fixed (for example, 1:1),and the multiplication may be omitted. In the superposition of the firstmodulated symbol stream and the second modulated symbol stream, anamplitude ratio constituted by a proportion of the first modulatedsymbol stream, a proportion of the real component of the secondmodulated symbol stream, and a proportion of the imaginary component ofthe second modulated symbol stream may be used as the predeterminedamplitude ratio. The proportion of one of the real component and theimaginary component that is not included in the first modulated symbolstream may be higher than the proportion of the other. Note that theproportion can also be represented as weight.

The following shows an example case in which BPSK is used as the firstmapping scheme to describe the operation of converter 1225.

For example, when S₁(t) is the t-th modulated symbol in the firstmodulated symbol stream generated by mapper 1213, and b₁(t) is a bit tobe mapped onto S₁(t), modulated symbol S₁(t) is given by Equation 16.[Math. 16]S ₁(t)=2·b ₁(t)−1  (Equation 16)

Modulated symbol S₁(t) may also be given by an equation in which the(positive/negative) polarity in Equation 16 is reversed. Converter 1225converts, into S′₂(t), the t-th modulated symbol S₂(t) in the secondmodulated symbol stream generated by mapper 1223, on the basis of b₁(t)as shown by Equation 17.[Math. 17]S′ ₂(t)=(−1)^(b) ¹ ^((t))·Re[S ₂(t)]+i·Im[S ₂(t)]  (Equation 1)

Here, S′₂(t) is the converted t-th modulated symbol in the secondmodulated symbol stream. Further, i denotes the imaginary unit.Re[S₂(t)] is the value of the real part of S₂(t), and Im[S₂(t)] is thevalue of the imaginary part of S₂(t). Modulated symbol S′₂(t) may begiven by an equation in which one of or both of the polarities of thereal part and the imaginary part of Equation 17 are reversed.

As described above, the polarity of the real part of each secondmodulated symbol is controlled in accordance with the values of the bitsto be mapped onto the first modulated symbol that is superposed withsuch a second modulated symbol. Note that the polarity of the real partof each second modulated symbol may be controlled in accordance with thefirst modulated symbol that is superposed with such a second modulatedsymbol.

In the above, superposition coding is performed on the real part.Accordingly, a first modulated symbol is constituted by a realcomponent, and the real component of the first modulated symbol and thereal component of a second modulated symbol are superposed on a singlereal component. However, superposition coding may be performed on theimaginary part. Accordingly, a first modulated symbol may be constitutedby an imaginary component, and the imaginary component of the firstmodulated symbol and the imaginary component of a second modulatedsymbol may be superposed on a single real component.

FIG. 25 shows an example configuration of transmission device 1300 thatmultiplexes two data series onto two layers by the variation ofsuperposition coding, and transmits the multiplexed data series. Theconfiguration of transmission device 1300 is different from theconfiguration of transmission device 1200. The configuration andoperation of transmission device 1300 will be described with referenceto FIG. 25.

Transmission device 1300 includes encoder 1311, interleaver 1312, mapper1313, multiplier 1314, encoder 1321, interleaver 1322, mapper 1323,converter 1325, multiplier 1324, adder 1330, and RF unit 1340. Thesestructural components may also be implemented as dedicated orgeneral-purpose circuits. Multiplier 1314, multiplier 1324, and adder1330 can also be represented collectively as a superposer. RF unit 1340can also be represented as a transmitter. RF unit 1340 may include anantenna.

Encoder 1311 encodes an inputted first data series on the basis of afirst error control coding scheme to generate a first bit stream.Interleaver 1312 permutes the bits in the first bit stream generated byencoder 1311 on the basis of a first permutation rule. Such permutationis also referred to as interleaving.

Mapper 1313 maps the first bit stream permuted by interleaver 1312 inaccordance with a first mapping scheme to generate a first modulatedsymbol stream that includes a plurality of first modulated symbols. Inthe mapping in accordance with the first mapping scheme, mapper 1313maps each group of bits that includes a first number of bits in thefirst bit stream onto one of the signal points in a first constellationin accordance with the values of such a group of bits.

Encoder 1321 encodes an inputted second data series on the basis of asecond error control coding scheme to generate a second bit stream.Interleaver 1322 permutes the bits in the second bit stream generated byencoder 1321 on the basis of a second permutation rule. Such permutationis also referred to as interleaving.

Mapper 1323 maps the second bit stream permuted by interleaver 1322 inaccordance with a second mapping scheme to generate a second modulatedsymbol stream that includes a plurality of second modulated symbols. Inthe mapping in accordance with the second mapping scheme, mapper 1323maps each group of bits that includes a second number of bits in thesecond bit stream onto one of the signal points in a secondconstellation in accordance with the values of such a group of bits.

Converter 1325 converts each second modulated symbol to be superposedwith the corresponding first modulated symbol, on the basis of thegenerated first modulated symbol. Through this, converter 1325 convertsthe second modulated symbol stream.

Multiplier 1314 multiplies each first modulated symbol in the firstmodulated symbol stream by first amplitude coefficient a₁. Multiplier1324 multiplies, by second amplitude coefficient a₂, each secondmodulated symbol in the second modulated symbol stream converted byconverter 1325.

Multiplier 1324 may multiply both the real part and the imaginary partof a second modulated symbol by second amplitude coefficient a₂, or maymultiply only one of the real part and the imaginary part by secondamplitude coefficient a₂. Alternatively multiplier 1324 may multiply thereal part and the imaginary part of a second modulated symbol bydifferent amplitude coefficients.

For example, when the first modulated symbol is constituted by only areal part, multiplier 1324 may multiply only the real part of a secondmodulated symbol by second amplitude coefficient a₂. Multiplier 1324does not need to multiply the imaginary part of the second modulatedsymbol by an amplitude coefficient, or may multiply the imaginary partby an amplitude coefficient smaller than second amplitude coefficienta₂.

Adder 1330 superposes first modulated symbols multiplied by firstamplitude coefficient a₁ and second modulated symbols multiplied bysecond amplitude coefficient a₂ to generate a superposed modulatedsymbol stream that includes a plurality of superposed modulated symbols.

RF unit 1340 sends the generated superposed modulated symbol stream as asignal. More specifically, RF unit 1340 generates, from the superposedmodulated symbol stream generated by adder 1330, a radio-frequencysignal as a signal corresponding to the superposed modulated symbolstream to send such a radio-frequency signal from the antenna.

Stated differently, the superposer constituted by multiplier 1314,multiplier 1324, and adder 1330 superposes the first modulated symbolstream and the second modulated symbol stream at a predeterminedamplitude ratio, thereby generating a multiplexed signal into which thefirst data series and the second data series are multiplexed.Subsequently, RF unit 1340 sends the multiplexed signal. Note that themultiplexed signal corresponds to the superposed modulated symbolstream.

Also the predetermined amplitude ratio may be fixed (for example, 1:1),and the multiplication may be omitted. In the superposition of the firstmodulated symbol stream and the second modulated symbol stream, anamplitude ratio constituted by a proportion of the first modulatedsymbol stream, a proportion of the real component of the secondmodulated symbol stream, and a proportion of the imaginary component ofthe second modulated symbol stream may be used as the predeterminedamplitude ratio. The proportion of one of the real component and theimaginary component that is not included in the first modulated symbolstream may be higher than the proportion of the other. Note that theproportion can also be represented as weight.

The following shows an example case in which BPSK is used as the firstmapping scheme to describe the operation of converter 1325.

For example, when S₁(t) is the t-th modulated symbol in the firstmodulated symbol stream generated by mapper 1313, and b₁(t) is a bit tobe mapped onto S₁(t), modulated symbol S₁(t) is given by Equation 18.[Math. 18]S ₁(t)=2·b ₁(t)−1  (Equation 18)

Modulated symbol S₁(t) may also be given by an equation in which thepolarity in Equation 18 is reversed. Converter 1325 converts, intoS′₂(t), t-th modulated symbol S₂(t) in the second modulated symbolstream generated by mapper 1323, on the basis of modulated symbol S₁(t)as shown by Equation 19.[Math. 19]S′ ₂(t)=sgn(S ₁(t))·Re[S ₂(t)]+i·Im[S ₂(t)]  (Equation 19)

Here, i denotes the imaginary unit. S′₂(t) is the converted t-thmodulated symbol in the second modulated symbol stream. Re[S₂(t)] is thevalue of the real part of S₂(t), and Im[S₂(t)] is the value of theimaginary part of S₂(t). Also, sgn(S₁(t)) is the polarity of S₁(t).

Modulated symbol S′₂(t) may be given by an equation in which one of orboth of the polarities of the real part and the imaginary part ofEquation 19 are reversed. Note that the conversion that is based onEquation 19 is substantially the same as the conversion that is based onEquation 17.

As described above, the polarity of the real part of each secondmodulated symbol is controlled in accordance with the first modulatedsymbol that is superposed with such a second modulated symbol. Note thatthe polarity of the real part of each second modulated symbol may becontrolled in accordance with the values of the bits to be mapped ontothe first modulated symbol that is superposed with such a secondmodulated symbol.

In the above, superposition coding is performed on the real part.Accordingly, a first modulated symbol is constituted by a realcomponent, and the real component of the first modulated symbol and thereal component of a second modulated symbol are superposed on a singlereal component. However, superposition coding may be performed on theimaginary part. Accordingly, a first modulated symbol may be constitutedby an imaginary component, and the imaginary component of the firstmodulated symbol and the imaginary component of a second modulatedsymbol may be superposed on a single real component.

FIG. 26 shows an example configuration of transmission device 1400 thatmultiplexes two data series onto two layers by the variation ofsuperposition coding, and transmits the multiplexed data series. Theconfiguration of transmission device 1400 is different from theconfigurations of transmission devices 1200 and 1300. The configurationand operation of transmission device 1400 will be described withreference to FIG. 26.

Transmission device 1400 includes encoder 1411, interleaver 1412, mapper1413, multiplier 1414, encoder 1421, interleaver 1422, mapper 1423,multiplier 1424, adder 1430, and RF unit 1440. These structuralcomponents may also be implemented as dedicated or general-purposecircuits. Multiplier 1414, multiplier 1424, and adder 1430 can also berepresented collectively as a superposer. RF unit 1440 can also berepresented as a transmitter. RF unit 1440 may include an antenna.Mapper 1423 may include a converter.

Encoder 1411 encodes an inputted first data series on the basis of afirst error control coding scheme to generate a first bit stream.Interleaver 1412 permutes the bits in the first bit stream generated byencoder 1411 on the basis of a first permutation rule. Such permutationis also referred to as interleaving.

Mapper 1413 maps the first bit stream permuted by interleaver 1412 inaccordance with a first mapping scheme to generate a first modulatedsymbol stream that includes a plurality of first modulated symbols. Inthe mapping in accordance with the first mapping scheme, mapper 1413maps each group of bits that includes a first number of bits in thefirst bit stream onto one of the signal points in a first constellationin accordance with the values of such a group of bits.

Encoder 1421 encodes an inputted second data series on the basis of asecond error control coding scheme to generate a second bit stream.Interleaver 1422 permutes the bits in the second bit stream generated byencoder 1421 on the basis of a second permutation rule. Such permutationis also referred to as interleaving.

Mapper 1423 converts (modifies) a second mapping scheme in accordancewith the first bit stream to be mapped to the first modulated symbolstream by mapper 1413. Mapper 1423 then maps the second bit streaminterleaved by interleaver 1422 in accordance with the second mappingscheme that has been converted in accordance with the first bit stream.Through these processes, mapper 1423 generates a second modulated symbolstream that includes a plurality of second modulated symbols.

In the mapping in accordance with the second mapping scheme, mapper 1423maps each group of bits that includes a second number of bits in thesecond bit stream onto one of the signal points in a secondconstellation in accordance with the values of such a group of bits.

Multiplier 1414 multiplies each first modulated symbol in the firstmodulated symbol stream by first amplitude coefficient a₁. Multiplier1424 multiplies each second modulated symbol in the second modulatedsymbol stream by second amplitude coefficient a₂.

Multiplier 1424 may multiply both the real part and the imaginary partof a second modulated symbol by second amplitude coefficient a₂, or maymultiply only one of the real part and the imaginary part by secondamplitude coefficient a₂. Alternatively, multiplier 1424 may multiplythe real part and the imaginary part of a second modulated symbol bydifferent amplitude coefficients.

For example, when a first modulated symbol is constituted by only a realpart, multiplier 1424 may multiply only the real part of a secondmodulated symbol by second amplitude coefficient a₂. Multiplier 1424does not need to multiply the imaginary part of the second modulatedsymbol by an amplitude coefficient, or may multiply the imaginary partby an amplitude coefficient smaller than second amplitude coefficienta₂.

Adder 1430 superposes first modulated symbols multiplied by firstamplitude coefficient a₁ and second modulated symbols having the realparts multiplied by second amplitude coefficient a₂ to generate asuperposed modulated symbol stream that includes a plurality ofsuperposed modulated symbols.

RF unit 1440 sends the generated superposed modulated symbol stream as asignal. More specifically, RF unit 1440 generates, from the superposedmodulated symbol stream generated by adder 1430, a radio-frequencysignal as a signal corresponding to the superposed modulated symbolstream to send such a radio-frequency signal from the antenna.

Stated differently, the superposer constituted by multiplier 1414,multiplier 1424, and adder 1430 superposes the first modulated symbolstream and the second modulated symbol stream at a predeterminedamplitude ratio, thereby generating a multiplexed signal into which thefirst data series and the second data series are multiplexed.Subsequently, RF unit 1440 sends the multiplexed signal. Note that themultiplexed signal corresponds to the superposed modulated symbolstream.

Also the predetermined amplitude ratio may be fixed (for example, 1:1),and the multiplication may be omitted. In the superposition of the firstmodulated symbol stream and the second modulated symbol stream, anamplitude ratio constituted by a proportion of the first modulatedsymbol stream, a proportion of the real component of the secondmodulated symbol stream, and a proportion of the imaginary component ofthe second modulated symbol stream may be used as the predeterminedamplitude ratio. The proportion of one of the real component and theimaginary component that is not included in the first modulated symbolstream may be higher than the proportion of the other. Note that theproportion can also be represented as weight.

The following shows an example case in which BPSK is used as the firstmapping scheme to describe the operation of mapper 1423.

For example, when S₁(t) is the t-th modulated symbol in the firstmodulated symbol stream generated by mapper 1413, and b₁(t) is a bit tobe mapped onto S₁(t), modulated symbol S₁(t) is given by Equation 20.[Math. 20]S ₁(t)=2·b ₁(t)−1  (Equation 20)

Modulated symbol stream S₁(t) may also be given by an equation in whichthe polarity in Equation 20 is reversed. Mapper 1423 performsexclusive-OR between b₁(t) and the bit that most contributes to the realpart of the second constellation among the bits in the second bit streaminputted from interleaver 1422. Mapper 1423 then maps the second bitstream on which exclusive-OR has been performed, on the basis of thesecond constellation.

Here, the bit that most contributes to the real part of the secondconstellation is a bit that causes the polarity of the real part of thesecond constellation to be reversed, for example, when the value of sucha bit is reversed from 0 to 1 or from 1 to 0. Stated differently, thebit that most contributes to the real part of the second constellationrefers to a bit that causes the negative/positive sign of the value ofthe real part of each modulated symbol to be reversed, for example, whenthe value of such a bit is reversed from 0 to 1 or from 1 to 0.

In the above description, mapper 1423 converts the second bit stream,thereby substantially converting the second mapping scheme (the secondconstellation). However, mapper 1423 may directly convert the secondmapping scheme (the second constellation) without converting the secondbit stream. Stated differently, mapper 1423 may convert thecorrespondence between groups of bits and signal points in the secondconstellation.

Also, the conversion performed by mapper 1423 may be performed by theconverter included in mapper 1423.

As described above, the polarity of the real part of each secondmodulated symbol is controlled in accordance with the values of the bitsto be mapped onto the first modulated symbol that is superposed withsuch a second modulated symbol. Note that the polarity of the real partof each second modulated symbol may be controlled in accordance with thefirst modulated symbol that is superposed with such a second modulatedsymbol.

In the above, superposition coding is performed on the real part.Accordingly, a first modulated symbol is constituted by a realcomponent, and the real component of the first modulated symbol and thereal component of a second modulated symbol are superposed on a singlereal component. However, superposition coding may be performed on theimaginary part. Accordingly, a first modulated symbol may be constitutedby an imaginary component, and the imaginary component of the firstmodulated symbol and the imaginary component of a second modulatedsymbol may be superposed on a single imaginary component.

<Sequential Decoding of Signal Obtained by Variation of SuperpositionCoding>

FIG. 27 shows an example configuration of reception device 1500 capableof receiving and sequentially decoding the signal on which two dataseries are multiplexed onto two layers by the above-described variationof superposition coding, and capable of obtaining one of or both of themultiplexed two data series. The configuration and operation ofreception device 1500 will be described with reference to FIG. 27.

Reception device 1500 includes RF unit 1530, demapper 1511,deinterleaver 1512, decoder 1513, encoder 1514, interleaver 1515, mapper1516, multiplier 1517, delayer 1518, subtractor 1519, converter 1520,demapper 1521, deinterleaver 1522, and decoder 1523. These structuralcomponents may also be implemented as dedicated or general-purposecircuits.

Demapper 1511, deinterleaver 1512, decoder 1513, encoder 1514,interleaver 1515, mapper 1516, multiplier 1517, delayer 1518, subtractor1519, converter 1520, demapper 1521, deinterleaver 1522, and decoder1523 can also be represented collectively as a deriver. RF unit 1530 canalso be represented as a receiver. RF unit 1530 may include an antenna.

Reception device 1500 receives by an antenna the multiplexed signal sentfrom transmission device 1200, 1300, or 1400, and inputs such amultiplexed signal into RF unit 1530. Stated differently, RF unit 1530receives the multiplexed signal via the antenna. The multiplexed signalreceived by RF unit 1530 is also represented as a received signal, andcorresponds to the superposed modulated symbol stream into which thefirst modulated symbol stream and the second modulated symbol stream aremultiplexed. RF unit 1530 generates a baseband received signal from theradio-frequency received signal.

Demapper 1511 demaps the baseband received signal on the basis of thefirst constellation of the first mapping scheme to generate the firstbit likelihood stream. For example, amplitude coefficient a₁ isreflected in the first constellation for demapping.

Deinterleaver 1512 permutes the first bit likelihood stream on the basisof a permutation rule that is a reverse rule of the first permutationrule. Such permutation is also referred to as deinterleaving. Decoder1513 performs decoding that is based on the first error control codingscheme by use of the first bit likelihood stream permuted bydeinterleaver 1512, and outputs the decoding result as the first dataseries.

Here, of the received signal corresponding to the superposed modulatedsymbol stream, demapper 1511 treats the components corresponding to thesecond modulated symbols in the second data series as an unknown signal(noise), and performs demapping on the basis of the first constellationof the first mapping scheme.

When only the first data series is to be obtained, reception device 1500terminates the process upon completing the estimation of the first dataseries. Meanwhile, when the second data series is to be obtained inaddition to the first data series, or when only the second data seriesis to be obtained, reception device 1500 performs the processesdescribed below to obtain the second data series.

Encoder 1514 encodes the first data series obtained by decoder 1513 onthe basis of the first error control coding scheme to generate the firstbit stream. Interleaver 1515 permutes the bits in the first bit streamgenerated by encoder 1514 on the basis of the first permutation rule.Such permutation is also referred to as interleaving.

Mapper 1516 maps the first bit stream permuted by interleaver 1515 inaccordance with the first mapping scheme to generate the first modulatedsymbol stream that includes a plurality of first modulated symbols.Multiplier 1517 multiplies the first modulated symbol stream outputtedby mapper 1516 by first amplitude coefficient a₁.

Delayer 1518 delays the received signal outputted from RF unit 1530during the time from when RF unit 1530 outputs the baseband receivedsignal to when multiplier 1517 outputs the reproduced first modulatedsymbol stream.

Subtractor 1519 subtracts, from the received signal delayed by delayer1518, the first modulated symbol stream multiplied by first amplitudecoefficient a₁ by multiplier 1517. Through this, subtractor 1519 removesthe components corresponding to the first modulated symbols from thereceived signal on which the components corresponding to the firstmodulated symbols, the components corresponding to the second modulatedsymbols, and noise are superposed. Subsequently, subtractor 1519 outputsa signal on which the components corresponding to the second modulatedsymbols and noise are superposed as a signal corresponding to the secondmodulated symbol stream.

Converter 1520 converts the signal outputted from subtractor 1519 as asignal corresponding to the second modulated symbol stream by use of thefirst bit stream reproduced through encoding, interleaving, etc.Demapper 1521 demaps the signal outputted by converter 1520 on the basisof the second constellation of the second mapping scheme to generate thesecond bit likelihood stream. For example, amplitude coefficient a₂ isreflected in the second constellation for demapping.

Deinterleaver 1522 permutes the second bit likelihood stream on thebasis of a permutation rule that is a reverse rule of the secondpermutation rule. Such permutation is also referred to asdeinterleaving. Decoder 1523 decodes the second bit likelihood streampermuted by deinterleaver 1522 on the basis of the second error controlcoding scheme, and outputs the decoding result as the second dataseries.

The following shows an example case in which BPSK is used as the firstmapping scheme to describe the operation of converter 1520.

For example, when S₁(t) is the t-th modulated symbol in the firstmodulated symbol stream generated by mapper 1516, and b₁(t) is a bit tobe mapped onto S₁(t), modulated symbol S₁(t) is given by Equation 21.[Math. 21]S ₁(t)=2·b ₁(t)−1  (Equation 21)

Modulated symbol S₁(t) may also be given by an equation in which thepolarity in Equation 21 is reversed. Converter 1520 converts, intoS′₂(t), signal S₂(t) corresponding to the t-th modulated symbol in thesecond modulated symbol stream among signals outputted by subtractor1519, on the basis of b as shown by Equation 22.[Math. 22]S′ ₂(t)=(−1)^(b) ¹ ^((t))·Re[S ₂(t)]+t·Im[S ₂(t)]  (Equation 22)

Here, i denotes the imaginary unit. Further, S′₂(t) is the signal thathas undergone the conversion. Also, Re[S₂(t)] is the value of the realpart of S₂(t), and Im[S₂(t)] is the value of the imaginary part ofS₂(t). Signal S′₂(t) that has undergone the conversion may be given byan equation in which one of or both of the polarities of the real partand the imaginary part of Equation 22 are reversed.

Through the above processes, reception device 1500 obtains one of orboth of the first data series and the second data series from the signalreceived by the antenna. Note that in the above, superposition coding isperformed on the real part. However, superposition coding may beperformed on the imaginary part.

FIG. 28 shows an example configuration of reception device 1600 capableof receiving and sequentially decoding the signal on which two dataseries are multiplexed onto two layers by the above-described variationof superposition coding, and capable of obtaining one of or both of themultiplexed two data series. The configuration of reception device 1600is different from the configuration of reception device 1500. Theconfiguration and operation of reception device 1600 will be describedwith reference to FIG. 28.

Reception device 1600 includes RF unit 1630, demapper 1611,deinterleaver 1612, decoder 1613, encoder 1614, interleaver 1615, mapper1616, multiplier 1617, delayer 1618, subtractor 1619, converter 1620,demapper 1621, deinterleaver 1622, and decoder 1623. These structuralcomponents may also be implemented as dedicated or general-purposecircuits.

Demapper 1611, deinterleaver 1612, decoder 1613, encoder 1614,interleaver 1615, mapper 1616, multiplier 1617, delayer 1618, subtractor1619, converter 1620, demapper 1621, deinterleaver 1622, and decoder1623 can also be represented collectively as a deriver. RF unit 1630 canalso be represented as a receiver. RF unit 1630 may include an antenna.

Reception device 1600 receives by an antenna the multiplexed signal sentfrom transmission device 1200, 1300, or 1400, and inputs such amultiplexed signal into RF unit 1630. Stated differently, RF unit 1630receives the multiplexed signal via the antenna. The multiplexed signalreceived by RF unit 1630 is also represented as a received signal, andcorresponds to the superposed modulated symbol stream into which thefirst modulated symbol stream and the second modulated symbol stream aremultiplexed. RF unit 1630 generates a baseband received signal from theradio-frequency received signal.

Demapper 1611 demaps the baseband received signal on the basis of thefirst constellation of the first mapping scheme to generate the firstbit likelihood stream. For example, amplitude coefficient a₁ isreflected in the first constellation for demapping.

Deinterleaver 1612 permutes the first bit likelihood stream on the basisof a permutation rule that is a reverse rule of the first permutationrule. Such permutation is also referred to as deinterleaving. Decoder1613 performs decoding that is based on the first error control codingscheme by use of the first bit likelihood stream permuted bydeinterleaver 1612, and outputs the decoding result as the first dataseries.

Here, of the received signal corresponding to the superposed modulatedsymbol stream, demapper 1611 treats the components corresponding to thesecond modulated symbols in the second data series as an unknown signal(noise), and performs demapping on the basis of the first constellationof the first mapping scheme.

When only the first data series is to be obtained, reception device 1600terminates the process upon completing the estimation of the first dataseries. Meanwhile, when the second data series is to be obtained inaddition to the first data series, or when only the second data seriesis to be obtained, reception device 1600 performs the processesdescribed below to obtain the second data series.

Encoder 1614 encodes the first data series obtained by decoder 1613 onthe basis of the first error control coding scheme to generate the firstbit stream. Interleaver 1615 permutes the bits in the first bit streamgenerated by encoder 1614 on the basis of the first permutation rule.Such permutation is also referred to as interleaving.

Mapper 1616 maps the first bit stream permuted by interleaver 1615 inaccordance with the first mapping scheme to generate the first modulatedsymbol stream that includes a plurality of first modulated symbols.Multiplier 1617 multiplies the first modulated symbol stream outputtedby mapper 1616 by first amplitude coefficient a₁.

Delayer 1618 delays the received signal outputted from RF unit 1630during the time from when RF unit 1630 outputs the baseband receivedsignal to when multiplier 1617 outputs the reproduced first modulatedsymbol stream.

Subtractor 1619 subtracts, from the received signal delayed by delayer1618, the first modulated symbol stream multiplied by first amplitudecoefficient a₁ by multiplier 1617. Through this, subtractor 1619 removesthe components corresponding to the first modulated symbols from thereceived signal on which the components corresponding to the firstmodulated symbols and the components corresponding to the secondmodulated symbols and noise are superposed. Subsequently, subtractor1619 outputs a signal on which the components corresponding to thesecond modulated symbols and noise are superposed as a signalcorresponding to the second modulated symbol stream.

Converter 1620 converts the signal outputted from subtractor 1619 as asignal corresponding to the second modulated symbol stream by use of thefirst modulated symbol stream reproduced through encoding, interleaving,mapping, etc. Demapper 1621 demaps the signal outputted by converter1620 on the basis of the second constellation of the second mappingscheme to generate the second bit likelihood stream. For example,amplitude coefficient a₂ is reflected in the second constellation fordemapping.

Deinterleaver 1622 permutes the second bit likelihood stream on thebasis of a permutation rule that is a reverse rule of the secondpermutation rule. Such permutation is also referred to asdeinterleaving. Decoder 1623 decodes the second bit likelihood streampermuted by deinterleaver 1622 on the basis of the second error controlcoding scheme, and outputs the decoding result as the second dataseries.

The following shows an example case in which BPSK is used as the firstmapping scheme to describe the operation of converter 1620.

For example, when S₁(t) is the t-th modulated symbol in the firstmodulated symbol stream generated by mapper 1616, and b₁(t) is a bit tobe mapped onto S₁(t), modulated symbol S₁(t) is given by Equation 23.[Math. 23]S ₁(t)=2·b ₁(t)−1  (Equation 23)

Modulated symbol S₁(t) may also be given by an equation in which thepolarity in Equation 23 are reversed. Converter 1620 converts, intoS′₂(t), signal S₂(t) corresponding to the t-th modulated symbol in thesecond modulated symbol stream out of the signal outputted by subtractor1619, on the basis of modulated symbol S₁(t) as shown by Equation 24.[Math. 24]S′ ₂(t)=sgn(S ₁(t))·Re[S ₂(t)]+i Im[S ₂(t)]  (Equation 24)

Here, i denotes the imaginary unit. Further, S′₂(t) is the signal thathas undergone the conversion. Also, Re[S₂(t)] is the value of the realpart of S₂(t), and Im[S₂(t)] is the value of the imaginary part ofS₂(t). Also, sgn(S₁(t)) is the polarity of S₁(t). Signal S′₂(t) that hasundergone the conversion may be given by an equation in which one of orboth of the polarities of the real part and the imaginary part ofEquation 24 are reversed. Note that the conversion that is based onEquation 24 is substantially the same as the conversion that is based onEquation 22.

Through the above processes, reception device 1600 obtains one of orboth of the first data series and the second data series from the signalreceived by the antenna. Note that in the above, superposition coding isperformed on the real part, but may be performed on the imaginary part.

FIG. 29 shows an example configuration of reception device 1700 capableof receiving and sequentially decoding the signal on which two dataseries are multiplexed onto two layers by the above-described variationof superposition coding, and capable of obtaining one of or both of themultiplexed two data series. The configuration of reception device 1700is different from the configurations of reception devices 1500 and 1600.The configuration and operation of reception device 1700 will bedescribed with reference to FIG. 29.

Reception device 1700 includes RF unit 1730, demapper 1711,deinterleaver 1712, decoder 1713, encoder 1714, interleaver 1715, mapper1716, multiplier 1717, delayer 1718, subtractor 1719, demapper 1721,deinterleaver 1722, and decoder 1723. These structural components mayalso be implemented as dedicated or general-purpose circuits.

Demapper 1711, deinterleaver 1712, decoder 1713, encoder 1714,interleaver 1715, mapper 1716, multiplier 1717, delayer 1718, subtractor1719, demapper 1721, deinterleaver 1722, and decoder 1723 can also berepresented collectively as a deriver. RF unit 1730 can also berepresented as a receiver. RF unit 1730 may include an antenna. Demapper1721 may include a converter.

Reception device 1700 receives by an antenna the multiplexed signal sentfrom transmission device 1200, 1300, or 1400, and inputs such amultiplexed signal into RF unit 1730. Stated differently, RF unit 1730receives the multiplexed signal via the antenna. The multiplexed signalreceived by RF unit 1730 is also represented as a received signal, andcorresponds to the superposed modulated symbol stream into which thefirst modulated symbol stream and the second modulated symbol stream aremultiplexed. RF unit 1730 generates a baseband received signal from theradio-frequency received signal.

Demapper 1711 demaps the baseband received signal on the basis of thefirst constellation of the first mapping scheme to generate the firstbit likelihood stream. For example, amplitude coefficient a₁ isreflected in the first constellation for demapping.

Deinterleaver 1712 permutes the first bit likelihood stream on the basisof a permutation rule that is a reverse rule of the first permutationrule. Such permutation is also referred to as deinterleaving. Decoder1713 performs decoding that is based on the first error control codingscheme by use of the first bit likelihood stream permuted bydeinterleaver 1712, and outputs the decoding result as the first dataseries.

Here, of the received signal corresponding to the superposed modulatedsymbol stream, demapper 1711 treats the components corresponding to thesecond modulated symbols in the second data series as an unknown signal(noise), and performs demapping on the basis of the first constellationof the first mapping scheme.

When only the first data series is to be obtained, reception device 1700terminates the process upon completing the estimation of the first dataseries. Meanwhile, when the second data series is to be obtained inaddition to the first data series, or when only the second data seriesis to be obtained, reception device 1700 performs the processesdescribed below to obtain the second data series.

Encoder 1714 encodes the first data series obtained by decoder 1713 onthe basis of the first error control coding scheme to generate the firstbit stream. Interleaver 1715 permutes the bits in the first bit streamgenerated by encoder 1714 on the basis of the first permutation rule.Such permutation is also referred to as interleaving.

Mapper 1716 maps the first bit stream permuted by interleaver 1715 inaccordance with the first mapping scheme to generate the first modulatedsymbol stream that includes a plurality of first modulated symbols.Multiplier 1717 multiplies the first modulated symbol stream outputtedby mapper 1716 by first amplitude coefficient a₁.

Delayer 1718 delays the received signal outputted from RF unit 1730during the time from when RF unit 1730 outputs the baseband receivedsignal to when multiplier 1717 outputs the reproduced first modulatedsymbol stream.

Subtractor 1719 subtracts, from the received signal delayed by delayer1718, the first modulated symbol stream multiplied by first amplitudecoefficient a₁ by multiplier 1717. Through this, subtractor 1719 removesthe components corresponding to the first modulated symbols from thereceived signal on which the components corresponding to the firstmodulated symbols, the components corresponding to the second modulatedsymbols, and noise are superposed. Subsequently, subtractor 1719 outputsa signal on which the components corresponding to the second modulatedsymbols and noise are superposed as a signal corresponding to the secondmodulated symbol stream.

Demapper 1721 demaps the signal outputted from subtractor 1719 as asignal corresponding to the second modulated symbol stream on the basisof the second constellation of the second mapping scheme to generate thesecond bit likelihood stream. At this time, such a process reflects thefirst bit stream reproduced through encoding, interleaving, etc. Forexample, amplitude coefficient a₂ is reflected in the secondconstellation for demapping.

Deinterleaver 1722 permutes the second bit likelihood stream on thebasis of a permutation rule that is a reverse rule of the secondpermutation rule. Such permutation is also referred to asdeinterleaving. Decoder 1723 decodes the second bit likelihood streampermuted by deinterleaver 1722 on the basis of the second error controlcoding scheme, and outputs the decoding result as the second dataseries.

The following shows an example case in which BPSK is used as the firstmapping scheme to describe the operation of demapper 1721.

For example, when S₁(t) is the t-th modulated symbol in the firstmodulated symbol stream generated by mapper 1716, and b₁(t) is a bit tobe mapped onto SAX modulated symbol S₁(t) is given by Equation 25.[Math. 25]S ₁(t)=2·b ₁(t)−1  (Equation 25)Modulated symbol S₁(t) may also be given by an equation in which thepolarity in Equation 25 is reversed. Demapper 1721 demaps signal S₂(t)outputted from subtractor 1719 as a signal corresponding to the t-thmodulated symbol in the second modulated symbol stream on the basis ofthe second constellation of the second mapping scheme.

Demapper 1721 reverses the bit likelihood corresponding to the bit thatmost contributes to the real part of the second constellation inaccordance with b₁(t) among the bit likelihoods in the bit likelihoodstream obtained by demapping. For example, demapper 1721 performsexclusive-OR between b₁(t) and the bit likelihood corresponding to thebit that most contributes to the real part of the second constellationamong the bit likelihoods in the bit likelihood stream obtained bydemapping.

Demapper 1721 then outputs the bit likelihood stream that has undergonethe above-described reversal processes as the second bit likelihoodstream.

In the above description, demapper 1721 converts the bit likelihoodstream, thereby substantially converting the second mapping scheme (thesecond constellation). However, demapper 1721 may directly convert thesecond mapping scheme (the second constellation) without converting thebit likelihood stream. Stated differently, demapper 1721 may convert thecorrespondence between groups of bits and signal points in the secondconstellation.

Also, the conversion performed by demapper 1721 may be performed by theconverter included in demapper 1721.

Through the above processes, reception device 1700 obtains one of orboth of the first data series and the second data series from the signalreceived by the antenna. Note that in the above, superposition coding isperformed on the real part. However, superposition coding may beperformed on the imaginary part.

<Parallel Decoding of Signal Obtained by Variation of SuperpositionCoding>

The following describes a reception method for parallel decoding of asignal obtained by the variation of superposition coding according tothe present embodiment. The configuration of the transmission device isthe same as the configuration of transmission device 1200 shown in FIG.24, transmission device 1300 shown in FIG. 25, or transmission device1400 shown in FIG. 26, and thus will not be described. In paralleldecoding in the variation of superposition coding, the reception devicetreats the components of the modulated symbol stream in the first layeras an unknown signal (noise) to decode the second layer, withoutremoving the components of the modulated symbol stream in the firstlayer included in the received signal.

FIG. 30 shows an example configuration of reception device 1800 capableof receiving and performing parallel decoding on the signal on which twodata series are multiplexed onto two layers by the variation ofsuperposition coding, and capable of obtaining one of or both of themultiplexed two data series. The configuration and operation ofreception device 1800 will be described with reference to FIG. 30.

Reception device 1800 includes RF unit 1830, demapper 1810,deinterleaver 1812, decoder 1813, deinterleaver 1822, and decoder 1823.These structural components may also be implemented as dedicated orgeneral-purpose circuits. Demapper 1810, deinterleaver 1812, decoder1813, deinterleaver 1822, and decoder 1823 can also be representedcollectively as a deriver. RF unit 1830 can also be represented as areceiver. RF unit 1830 may include an antenna.

Reception device 1800 receives by an antenna the multiplexed signal sentfrom transmission device 1200, 1300, or 1400, and inputs such amultiplexed signal into RF unit 1830. Stated differently, RF unit 1830receives the multiplexed signal via the antenna. The multiplexed signalreceived by RF unit 1830 can also be represented as a received signal.RF unit 1830 generates a baseband received signal from theradio-frequency received signal.

Demapper 1810 demaps the baseband received signal to generate the firstbit likelihood stream and the second bit likelihood stream. For example,demapper 1810 performs demapping on the basis of a variationsuperposition constellation that shows the arrangement of signal pointsof superposed modulated symbols obtained by superposing the firstmodulated symbols and the second modulated symbols by the variation ofsuperposition coding.

The variation superposition constellation is determined in accordancewith the first constellation of the first mapping scheme, the secondconstellation of the second mapping scheme, first amplitude coefficienta₁, second amplitude coefficient a₂, etc.

FIG. 31 shows an example of a BPSK constellation. More specifically, twoBPSK signal points are plotted in the complex plane, with the lateralaxis representing the real part (the real component) and the verticalaxis representing the imaginary part (the imaginary component). Notethat BPSK means binary phase shift keying.

For example, in BPSK, a bit (0 or 1) is associated with a modulatedsymbol indicating a complex number on the basis of the constellationshown in FIG. 31. In this example, a bit is associated with a modulatedsymbol indicating a complex number whose imaginary part is 0.Specifically, in this example, a bit is substantially associated with amodulated symbol indicating a real number.

FIG. 32 shows the variation superposition constellation that supportsthe variation of superposition coding. More specifically, the variationsuperposition constellation is a combination of the BPSK constellationshown in FIG. 31 and the Nu-256QAM constellation shown in FIG. 5.

Even more specifically, the Nu-256QAM constellation (256 signal points)is placed on each of two regions in the complex plane in accordance withthe two signal points of the BPSK constellation. These two regions, eachcorresponding to Nu-256QAM constellation, may partially overlap witheach other. The present variation superposition constellation reflectsthe conversion performed on the second modulated symbol stream.

For example, when the Nu-256QAM constellation is combined with a signalpoint with a positive real part among the two signal points of the BPSKconstellation, the polarity of the real part of the Nu-256QAMconstellation is reversed. More specifically, a first signal point, asecond signal point, and a third signal point are shown in FIG. 32. Whenthe polarity of the real part of the Nu-256QAM constellation is notreversed, the first signal point and the third signal point correspondto the same bit values of the second bit stream.

When the polarity of the real part of the Nu-256QAM constellation isreversed, the first signal point and the second signal point correspondto the same bit values of the second bit stream. Stated differently,such reversal enables a plurality of signal points that correspond tothe same bit values of the second bit stream to approach each other andconverge. This mitigates the effect of noise on demapping.

Demapper 1810 performs demapping on the basis of the variationsuperposition constellation as shown in FIG. 32. Stated differently,demapper 1810 generates the first bit likelihood stream with themodulated symbol stream of the second layer remaining unknown, andgenerates the second bit likelihood stream with the modulated symbolstream of the first layer remaining unknown.

Note that demapper 1810 may use the first constellation of the firstmapping scheme to generate the first bit likelihood stream, and may usethe above-described variation superposition constellation to generatethe second bit likelihood stream.

The first constellation, when used to generate the first bit likelihoodstream, enables demapper 1810 to reduce the number of signal points thatshould be considered in generating the first bit likelihood stream,compared to when the variation superposition constellation is also usedto generate the first bit likelihood stream. This thus enables demapper1810 to reduce the number of arithmetic computations.

Demapper 1810 corresponds, for example, to the first demapper thatdemaps the received signal to generate the first bit likelihood streamand the second demapper that demaps the received signal to generate thesecond bit likelihood stream. Demapper 1810 may include the firstdemapper that demaps the received signal to generate the first bitlikelihood stream and the second demapper that demaps the receivedsignal to generate the second bit likelihood stream.

Demapper 1810 may convert the second bit likelihood stream that isgenerated using not the variation superposition constellation but thesuperposition constellation, in accordance with the first bit likelihoodstream. This enables demapper 1810 to obtain the same second bitlikelihood stream as the second bit likelihood stream that is generatedusing the variation superposition constellation.

Demapper 1810 may convert the multiplexed signal without using thevariation superposition constellation to obtain the same second bitlikelihood stream as the second bit likelihood stream that is generatedusing the variation superposition constellation.

Deinterleaver 1812 permutes the first bit likelihood stream on the basisof a permutation rule that is a reverse rule of the first permutationrule. Such permutation is also referred to as deinterleaving. Decoder1813 decodes the first bit likelihood stream permuted by deinterleaver1812 on the basis of the first error control coding scheme, and outputsthe decoding result as the first data series.

Deinterleaver 1822 permutes the second bit likelihood stream on thebasis of a permutation rule that is a reverse rule of the secondpermutation rule. Such permutation is also referred to asdeinterleaving. Decoder 1823 decodes the second bit likelihood streampermuted by deinterleaver 1822 on the basis of the second error controlcoding scheme, and outputs the decoding result as the second dataseries.

Through the above processes, reception device 1800 obtains one of orboth of the first data series and the second data series from the signalreceived by the antenna. Note that in the above, superposition coding isperformed on the real part. However, superposition coding may beperformed on the imaginary part.

Note that transmission devices 1200, 1300, and 1400, and receptiondevices 1500, 1600, 1700, and 1800 may omit permutation (interleavingand deinterleaving) as in the case of Embodiment 1. Stated differently,their respective interleavers and deinterleavers are optional structuralcomponents, and thus may not be included in these devices.

Interleaving and deinterleaving, however, make a pair. As such, whentransmission devices 1200, 1300, and 1400 include their respectiveinterleavers, reception devices 1500, 1600, 1700, and 1800 basicallyinclude their respective deinterleavers and interleavers. Meanwhile,when transmission devices 1200, 1300, and 1400 do not include theirrespective interleavers, reception devices 1500, 1600, 1700, and 1800 donot include their respective deinterleavers and interleavers.

Amplitude coefficient a₁ may be reflected in the mapping for generatingthe first modulated symbols performed in reception devices 1500, 1600,and 1700. In such a case, the multiplication of amplitude coefficient a₁may be omitted. Reception devices 1500, 1600, and 1700 thus may notinclude multipliers 1517, 1617, and 1717, respectively.

Error control coding on the first data series and the second data seriesmay be performed by an external device. In such a case, transmissiondevices 1200, 1300, and 1400 may omit error control coding, and may notinclude encoders 1211, 1221, 1311, 1321, 1411, and 1421.

As described above, superposition coding may be performed on the realpart or on the imaginary part. Furthermore, superposition coding may beperformed in a predetermined direction in the complex plane. Forexample, superposition coding may be performed in an oblique directionin an orthogonal coordinate system having a real axis and an imaginaryaxis.

Specifically, a first modulated symbol may include a component in thefirst direction in the complex plane, and a second modulated symbol mayinclude a component in the first direction and a component in the seconddirection perpendicular to the first direction. The component that afirst modulated symbol includes in the first direction and the componentthat a second modulated symbol includes in the first direction may besuperposed on a single component in the first direction. In this case,for example, the polarity of the component of the second modulatedsymbol in the first direction is controlled in accordance with thecomponent of the first modulated symbol in the first direction.

Specifically, in the description given herein, a real component may bereplaced with an imaginary component, replaced with a component in thefirst direction that is one direction in the complex plane, or replacedwith a component in the second direction perpendicular to the firstdirection. In addition, an imaginary component may be replaced with areal component, replaced with a component in the first direction that isone direction in the complex plane, or replaced with a component in thesecond direction perpendicular to the first direction.

For example, a component that a modulated symbol includes in the firstdirection includes a real part and an imaginary part, and the polarityof such a component is reversed, thus reversing both of the polaritiesof the real and imaginary parts of the component. Furthermore, thepolarity of the component may be determined in accordance with thepolarity of the real part of the component or in accordance with thepolarity of the imaginary part of the component.

Specifically, when the polarity of the real part of the component ispositive, the polarity of the component may be determined to bepositive, and when the polarity of the real part of the component isnegative, the polarity of the component may be determined to benegative. Alternatively, when the polarity of the imaginary part of thecomponent is positive, the polarity of the component may be determinedto be positive, and when the polarity of the imaginary part of thecomponent is negative, the polarity of the component may be determinedto be negative.

Furthermore, the direction of the real axis may be the first directionor may be the second direction perpendicular to the first direction. Thedirection of the imaginary axis may be the first direction or may be thesecond direction perpendicular to the first direction.

The first constellation of the first mapping scheme may have a pluralityof signal points dispersed in only the first direction. Furthermore, thesecond constellation of the second mapping scheme may have a pluralityof signal points dispersed in both the first direction and the seconddirection.

The first mapping scheme is not limited to BPSK. A constellation havingthree or more signal points may be used as the first constellation ofthe first mapping scheme. For example, a constellation having three ormore signal points on a straight line in the complex plane may be usedas the first constellation of the first mapping scheme.

In the first constellation of the first mapping scheme, the polarity inthe first direction of the second mapping scheme is reversed for twosignal points adjacent to each other along a straight line in the firstdirection. Specifically, the polarity is reversed such that a secondmodulated symbol superposed on a first modulated symbol corresponding toone of the two signal points and a second modulated symbol superposed ona first modulated symbol corresponding to the other have differentpolarities in the first direction. Thus, the polarities in the firstdirection are alternated along a sequence of three or more signal pointson a straight line in the first direction.

FIG. 33 is a flowchart of example operations performed by transmissiondevice 1200. First, mapper 1213 maps the first bit stream of the firstdata series to generate the first modulated symbol stream of the firstdata series (S501). Then, mapper 1223 maps the second bit stream of thesecond data series to generate the second modulated symbol stream of thesecond data series (S502).

Converter 1225 subjects the second modulated symbol stream to conversionin accordance with the first modulation symbol stream, in only the firstdirection among the first direction and the second direction (S503).Here, the first direction and the second direction are two directionsperpendicular to each other in the complex plane in which the firstmodulated symbol stream and the second modulated symbol stream arerepresented.

Specifically, converter 1225 does not subject a component that thesecond modulated symbol stream includes in the second direction toconversion in accordance with the first modulation symbol stream, butsubjects a component that the second modulated symbol stream includes inthe first direction to the conversion. Furthermore, converter 1225converts the second modulated symbol stream in accordance with the firstbit stream, thereby subjecting the second modulated symbol stream toconversion in accordance with the first modulated symbol stream.

Next, the superposer superposes the first modulated symbol stream andthe second modulated symbol stream that has been subjected to conversionin accordance with the first modulated symbol stream at a predeterminedamplitude ratio, thereby generating the multiplexed signal (S504). Here,the superposer is constituted by first multiplier 1214, secondmultiplier 1224, and adder 1230. RF unit 1240 then sends the generatedmultiplexed signal (S505).

Note that in the above operation example, transmission device 1200converts the second modulated symbol stream in accordance with the firstbit stream, thereby subjecting the second modulated symbol stream toconversion in accordance with the first modulated symbol stream (S503).Alternatively, transmission device 1200 may convert the second modulatedsymbol stream in accordance with the first modulated symbol stream, asin the case of transmission device 1300, thereby subjecting the secondmodulated symbol stream to conversion in accordance with the firstmodulated symbol stream.

Alternatively, as in the case of transmission device 1400, transmissiondevice 1200 may convert the second bit stream or the second mappingscheme (the second constellation) used to generate the second modulatedsymbol stream, in accordance with the first bit stream. Through this,the second modulated symbol stream may be subjected to conversion inaccordance with the first modulated symbol stream. In such a case, thesecond bit stream or the second mapping scheme is converted before thesecond modulated symbol stream is generated.

Stated differently, the second bit stream, the second mapping scheme, orthe second modulated symbol stream may be converted in accordance withthe first bit stream or the first modulated symbol stream, therebysubjecting the second modulated symbol stream to conversion inaccordance with the first modulated symbol stream.

Converter 1225 may subject the second modulated symbol stream toconversion in accordance with the first modulated symbol stream, therebycontrolling the polarity of a component that each modulated symbol inthe second modulated symbol stream includes in the first direction.Through this, converter 1225 may reverse the polarity of a componentthat each second modulated symbol includes in the first direction when acomponent that the corresponding first modulated symbol includes in thefirst direction satisfies a predetermined condition.

The predetermined condition may be a condition that the polarity of acomponent that the first modulated symbol includes in the firstdirection should be a predetermined polarity, or may be a condition thatthe component that the first modulated symbol includes in the firstdirection should be within a predetermined range of one or more. Thepredetermined range of one or more may be a positive range or a negativerange.

FIG. 34 is a flowchart of example operations performed by receptiondevices 1500, 1600, 1700, and 1800. First, the receiver receives themultiplexed signal (S601). Here, the receiver is RF unit 1530 ofreception device 1500, RF unit 1630 of reception device 1600, RF unit1730 of reception device 1700, or RF unit 1830 of reception device 1800.

The multiplexed signal is a signal into which a plurality of data seriesincluding the first data series in the first layer and the second dataseries in the second layer are multiplexed. The multiplexed signal isalso a signal on which the first modulated symbol stream and the secondmodulated symbol stream are superposed at a predetermined amplituderatio.

The first modulated symbol stream is a modulated symbol stream that isgenerated by mapping the first bit stream of the first data series. Thesecond modulated symbol stream is a modulated symbol stream that isgenerated by mapping the second bit stream of the second data series,and that has been subjected to conversion in accordance with the firstmodulated symbol stream in only the first direction among the firstdirection and the second direction in a complex plane.

Next, the deriver derives at least one of the first data series or thesecond data series from the multiplexed signal (S602).

The deriver of reception device 1500 is constituted, for example, bydemapper 1511, deinterleaver 1512, decoder 1513, encoder 1514,interleaver 1515, mapper 1516, multiplier 1517, delayer 1518, subtractor1519, converter 1520, demapper 1521, deinterleaver 1522, and decoder1523.

The deriver of reception device 1600 is constituted, for example, bydemapper 1611, deinterleaver 1612, decoder 1613, encoder 1614,interleaver 1615, mapper 1616, multiplier 1617, delayer 1618, subtractor1619, converter 1620, demapper 1621, deinterleaver 1622, and decoder1623.

The deriver of reception device 1700 is constituted, for example, bydemapper 1711, deinterleaver 1712, decoder 1713, encoder 1714,interleaver 1715, mapper 1716, multiplier 1717, delayer 1718, subtractor1719, demapper 1721, deinterleaver 1722, and decoder 1723.

The deriver of reception device 1800 is constituted, for example, bydemapper 1810, deinterleaver 1812, decoder 1813, deinterleaver 1822, anddecoder 1823.

In accordance with the above operations, the multiplexed signal isreceived into which the first modulated symbol stream and the secondmodulated symbol stream that has been subjected to conversion inaccordance with the first modulated symbol stream in the first directionare multiplexed. Then, at least one of the first data series or thesecond data series is derived from such a multiplexed signal. Stateddifferently, such a configuration enables: the reception of themultiplexed signal that has been superposed in such a manner thatreduces performance degradation at the time of parallel decoding: and anefficient derivation of one of or both of the first data series and thesecond data series from such a multiplexed signal.

Reception device 1800 as shown in FIG. 30 that performs paralleldecoding has lower performance in decoding the second layer than that ofreception devices 1500, 1600, and 1700 as shown in FIG. 27, FIG. 28, andFIG. 29 that perform sequential decoding.

As described above, reception device 1800 according to the presentembodiment that performs parallel decoding has lower performance indecoding the second data series transmitted on the second layer thanthat of reception devices 1500, 1600, and 1700 that perform sequentialdecoding. However, reception device 1800 reduces the number ofstructural components required to decode the second layer.

More specifically, reception device 1800 eliminates the need for thestructural components that are required by reception devices 1500, 1600,and 1700 shown in FIG. 27, FIG. 28, and FIG. 29 performing sequentialdecoding to reproduce the modulated symbol stream of the first layer.Stated differently, encoders 1514, 1614, and 1714, interleavers 1515,1615, and 1715, mappers 1516, 1616, and 1716, and multipliers 1517,1617, and 1717 are not required.

Reception device 1800 also eliminates the need for delayers 1518, 1618,and 1718 that delay the received signal, and subtractors 1519, 1619, and1719 that remove the components of the modulated symbols in the firstlayer reproduced from the received signal.

The circuit size can be thus reduced. Reception device 1800 alsorequires a smaller number of arithmetic computations and lower powerconsumption than those required by reception devices 1500, 1600, and1700.

Reception devices 1500, 1600, and 1700 shown in FIG. 27, FIG. 28, andFIG. 29 that perform sequential decoding demodulate the first layer inthe received signal to obtain the first data series, and generate thefirst modulated symbol stream from the obtained first data series.Subsequently, reception devices 1500, 1600, and 1700 start demodulatingthe second layer in the received signal to obtain the second dataseries.

Meanwhile, reception device 1800 according to the present embodimentthat performs parallel decoding is capable of simultaneously obtainingthe first data series and the second data series in parallel, therebyreducing processing delays.

The reception device may observe the SNR of the received signal to makeselection between parallel decoding to be performed when the SNR is highand sequential decoding to be performed when the SNR is low.

In such a case, reception device 1500 shown in FIG. 27 includes, forexample, a controller that makes selection between sequential decodingand parallel decoding depending on the SNR. Such a controller may beincluded in RF unit 1530 or demapper 1521. Furthermore, demapper 1521 isconfigured to perform demapping based on the variation superpositionconstellation, which is described as an operation performed by demapper1810 shown in FIG. 30, in addition to demapping that is based on thesecond constellation.

Demapper 1521 switches between demapping to be performed on the signaloutputted from converter 1520 on the basis of the second constellationand demapping to be performed on the signal outputted from RF unit 1530on the basis of the variation superposition constellation. For example,demapper 1521 switches between these demapping operations in accordancewith a control signal from the controller.

Note that such a configuration is also obtained by a combination ofreception device 400 shown in FIG. 11, reception device 1500 (converter1520, demapper 1521, etc.) shown in FIG. 27, and reception device 1800(demapper 1810, etc.) shown in FIG. 30.

Another configuration is that reception device 1600 shown in FIG. 28includes, for example, a controller that makes selection betweensequential decoding and parallel decoding depending on the SNR. Such acontroller may be included in RF unit 1630 or demapper 1621.Furthermore, demapper 1621 is configured to perform demapping based onthe variation superposition constellation, which is described as anoperation performed by demapper 1810 shown in FIG. 30, in addition todemapping that is based on the first bit stream and the secondconstellation.

Demapper 1621 switches between demapping to be performed on the signaloutputted from converter 1620 on the basis of the second constellationand demapping to be performed on the signal outputted from RF unit 1630on the basis of the variation superposition constellation. For example,demapper 1621 switches between these demapping operations in accordancewith a control signal from the controller.

Note that such a configuration is also obtained by a combination ofreception device 400 shown in FIG. 11, reception device 1600 (converter1620, demapper 1621, etc.) shown in FIG. 28, and reception device 1800(demapper 1810, etc.) shown in FIG. 30.

Still another configuration is that reception device 1700 shown in FIG.29 includes, for example, a controller that makes selection betweensequential decoding and parallel decoding depending on the SNR. Such acontroller may be included in RF unit 1730 or demapper 1721.Furthermore, demapper 1721 is configured to perform demapping based onthe variation superposition constellation, which is described as anoperation performed by demapper 1810 shown in FIG. 30, in addition todemapping that is based on the first bit stream and the secondconstellation.

Demapper 1721 switches between demapping to be performed on the signaloutputted from subtractor 1719 on the basis of the second constellationand demapping to be performed on the signal outputted from RF unit 1730on the basis of the variation superposition constellation. For example,demapper 1721 switches between these demapping operations in accordancewith a control signal from the controller.

Note that such a configuration is also obtained by a combination ofreception device 400 shown in FIG. 11, reception device 1700 (demapper1721, etc.) shown in FIG. 29, and reception device 1800 (demapper 1810,etc.) shown in FIG. 30.

As described above, reception devices 1500, 1600, and 1700 performparallel decoding when the SNR is high, thereby reducing the number ofarithmetic computations and power consumption. Reception devices 1500,1600, and 1700 also perform parallel decoding when the SNR is high,thereby reducing processing delays. Meanwhile, reception devices 1500,1600, and 1700 perform sequential decoding when the SNR is low, therebyincreasing the possibility of correctly decoding the second data series.

In the present embodiment, different mapping rules may be used for thereal part and the imaginary part in the second mapping scheme. Whensuperposition coding is performed on the real part, the receiving levelof the real part is lower than the receiving level of the imaginary partin the second mapping scheme. Accordingly, in the second mapping scheme,it is better that the noise tolerance of the real part is higher thanthe noise tolerance of the imaginary part.

Accordingly, it is suitable to make the multilevel number for mappingthe real part smaller than the multilevel number for mapping theimaginary part. A multilevel number is also referred to as a modulationmultilevel number. For example, 32-PAM may be used to map the real partin accordance with the second mapping scheme, and 64-PAM may be used tomap the imaginary part.

When a non-uniform constellation is used as the second constellation ofthe second mapping scheme, it is suitable to use a non-uniformconstellation in which the real part corresponds to an SNR lower thanthat of the imaginary part. For example, non-uniform 32-PAMcorresponding to an SNR of about 15 dB may be used to map the real partin accordance with the second mapping scheme, and non-uniform 32-PAMcorresponding to an SNR of about 20 dB may be used to map the imaginarypart.

Note that 32 indicated as the multilevel number for mapping the realpart and 64 indicated as the multilevel number for mapping the imaginarypart are mere examples and may be other values. For example, 4-PAM maybe used for the real part, and 8-PAM may be used for the imaginary part.Furthermore, 2-PAM may be used for the real part, and 4-PAM may be usedfor the imaginary part. Furthermore, 2-PAM may be used for the realpart, and 8-PAM may be used for the imaginary part. Thus, a combinationof any values may be used to map the real part and the imaginary part.

The second data series may include two series. Among the two series, abit stream in one series is mapped on the real part, and a bit stream inthe other series may be mapped on the imaginary part. One modulatedsymbol stream may be generated as the second modulated symbol stream bymapping the two bit streams in the two series on the real part and theimaginary part. In such a case, PAM that can be used as a single-axismodulation scheme is effective. Note that PAM means pulse amplitudemodulation.

FIG. 35 shows an example of a constellation based on PAM. Specifically,a plurality of signal points based on PAM are plotted in the complexplane, with the lateral axis representing the real part (the realcomponent) and the vertical axis representing the imaginary part (theimaginary component). In this example, non-uniform 8-PAM is used for thereal part and non-uniform 16-PAM is used for the imaginary part.

The constellation shown in FIG. 35 may be used as the secondconstellation of the second mapping scheme. Specifically, aconstellation in which more signal points are arranged in the verticalaxis direction corresponding to the imaginary part than in thehorizontal axis direction corresponding to the real part may be used asthe second constellation of the second mapping scheme.

FIG. 36 shows an example of the variation superposition constellationcorresponding to the variation of superposition coding. Specifically,the constellation shown in FIG. 31 and the constellation shown in FIG.35 are combined. Stated differently, a BPSK constellation and aconstellation based on PAM are combined. The first constellation of thefirst mapping scheme is the BPSK constellation, and the secondconstellation of the second mapping scheme is the constellation based onPAM.

More specifically, in accordance with two signal points in the BPSKconstellation, the constellation based on PAM (128 signal points) isplaced on each of two regions in the complex plane. The two regions,each corresponding to the constellation based on PAM, may partiallyoverlap each other.

In this example, first amplitude coefficient a₁ is a positive squareroot of 0.75, second amplitude coefficient a₂ is a positive square rootof 0.25, and two constellations are combined based on the amplitudecoefficients. Note that in superposition coding in this example, theimaginary part of the second modulated symbol stream is not multipliedby second amplitude coefficient a₂, and the value of the imaginary partat a signal point included in the second constellation that is aconstellation based on PAM is maintained.

The variation superposition constellation reflects the conversionperformed on the second modulated symbol stream. For example, when theconstellation based on PAM is combined with a signal point with apositive real part among two signal points in the BPSK constellation,the polarity of the real part in the constellation based on PAM isreversed.

Note that in the above second mapping scheme, the mapping rule for thereal part and the mapping rule for the imaginary part are based on PAM,yet the second mapping scheme may be a mapping scheme other than this.

For example, arbitrary QAM or arbitrary non-uniform QAM which hasarrangement of signal points each with the real part and the imaginarypart both represented by PAM of an arbitrary multilevel number may beused as the second mapping scheme. As another example, arbitrarynon-uniform QAM which has arrangement of signal points each with thereal part and the imaginary part either or both of which are notrepresented by PAM may be used as the second mapping scheme.

In this case, for example, the arrangement of signal points each withthe real part corresponding to an SNR of about 15 dB and the imaginarypart corresponding to an SNR of about 20 dB may be used for the secondmapping scheme. As another example, the arrangement of signal points inwhich the greatest value of the real components at the signal points issmaller than the greatest value of the imaginary components at thesignal points may be used as the second mapping scheme.

In the above, superposition coding is performed on the real part, yetprocessing on the real part and processing on the imaginary part may beswitched, and superposition coding may be performed on the imaginarypart. Stated differently, a first modulated symbol may be constituted bythe imaginary component, and the imaginary component of the firstmodulated symbol and the imaginary component of a second modulatedsymbol may be superposed on a single imaginary component.

In addition, the second modulated symbol stream is not necessarilysubjected to conversion in accordance with the first modulated symbolstream. Specifically, the polarity may not be reversed, and may not needto be controlled. Even if such conversion is not applied, simplesuperposition coding can be performed along the real axis, the imaginaryaxis, or one direction corresponding to another axis. Accordingly, thisprovides more flexible superposition coding.

Even if conversion is not applied, superposition coding is performedmore efficiently by use of a mapping scheme or a constellation accordingto the direction of superposition coding.

As described above, a transmission device according to an aspect of thepresent disclosure is a transmission device that multiplexes a pluralityof data series including a first data series in a first layer and asecond data series in a second layer, and transmits a multiplexed signalinto which the plurality of data series have been multiplexed, thetransmission device including: a first mapper that maps a first bitstream of the first data series to generate a first modulated symbolstream of the first data series; a second mapper that maps a second bitstream of the second data series to generate a second modulated symbolstream of the second data series; a converter that subjects the secondmodulated symbol stream to conversion in accordance with the firstmodulated symbol stream in only a first direction among the firstdirection and a second direction perpendicular to each other in acomplex plane in which the first modulated symbol stream and the secondmodulated symbol stream are represented; a superposer that superposesthe first modulated symbol stream and the second modulated symbol streamsubjected to the conversion, at a predetermined amplitude ratio, togenerate the multiplexed signal; and a transmitter that transmits themultiplexed signal.

Accordingly, for example, the transmission device can convert acomponent which each modulated symbol in the second modulated symbolstream of the second data series includes in the first direction, inaccordance with the first modulated symbol stream of the first dataseries. Accordingly, the transmission device can appropriately adjustthe second modulated symbol stream of the second data series, inaccordance with the first modulated symbol stream of the first dataseries, thus allowing the second data series to be readily derived fromthe multiplexed signal into which the first modulated symbol stream andthe second modulated symbol stream are multiplexed.

Accordingly, the transmission device can help inhibiting a processingdelay in the reception device, and can efficiently perform processing ina multiplexing scheme that utilizes superposition coding.

For example, the converter may control a polarity of a component thateach of modulated symbols in the second modulated symbol stream includesin the first direction, by subjecting the second modulated symbol streamto the conversion.

Accordingly, the transmission device can control the polarity of acomponent that each modulated symbol in the second modulated symbolstream includes in the first direction, in accordance with the firstmodulated symbol stream. Thus, the transmission device can superpose thefirst modulated symbol stream and the second modulated symbol stream inwhich the polarity of each modulated symbol in the first direction iscontrolled in accordance with the first modulated symbol stream. Stateddifferently, the transmission device can superpose the first modulatedsymbol stream and the second modulated symbol stream in which thepolarity is appropriately adjusted in accordance with the firstmodulated symbol stream.

For example, in superposing the first modulated symbol stream and thesecond modulated symbol stream, the superposer may superpose a firstmodulated symbol in the first modulated symbol stream and a secondmodulated symbol in the second modulated symbol stream in which thepolarity is controlled, and in controlling the polarity, when acomponent that the first modulated symbol includes in the firstdirection satisfies a predetermined condition, the converter may reversea polarity of a component that the second modulated symbol includes inthe first direction.

Accordingly, the transmission device can transmit the multiplexed signalon which the first modulated symbol and the second modulated symbol thepolarity of which in the first direction is reversed in accordance withthe first modulated symbol are superposed. The reversal of the polarityof the second modulated symbol brings a plurality of signal pointsassociated with the same bit group of the second data series close toeach other. Accordingly, the transmission device can more appropriatelyadjust the second modulated symbol stream of the second data series inaccordance with the first modulated symbol stream of the first dataseries, and allows the second data series to be readily derived from themultiplexed signal.

For example, the converter may subject the second modulated symbolstream to the conversion by converting the second bit stream, aconstellation used to map the second bit stream, or the second modulatedsymbol stream, in accordance with the first bit stream or the firstmodulated symbol stream.

Accordingly, the transmission device can convert informationcorresponding to the second modulated symbol stream in accordance withinformation corresponding to the first modulated symbol stream, and canappropriately subject the second modulated symbol stream to theconversion in accordance with the first modulated symbol stream.

For example, the first mapper may map the first bit stream by use of afirst constellation in which a plurality of signal points are dispersedin only the first direction among the first direction and the seconddirection, and the second mapper may map the second bit stream by use ofa second constellation in which a plurality of signal points aredispersed in both the first direction and the second direction.

Accordingly, the transmission device can apply superposition coding inthe first direction. Thus, the transmission device can superpose, on asingle component, a component that the first modulated symbol in thefirst modulated symbol stream includes in the first direction, and acomponent that the second modulated symbol in the second modulatedsymbol stream includes in the first direction. The transmission devicecan apply suitable superposition coding in the first direction, usingthe second modulated symbol stream adjusted with respect to the firstdirection.

For example, the second constellation used by the second mapper to mapthe second bit stream may be a constellation in which noise tolerance inthe first direction is higher than noise tolerance in the seconddirection.

Accordingly, the transmission device can inhibit the influence of noisetolerance which decreases due to superposition coding, for the firstdirection in which superposition coding is applied.

For example, the second constellation used by the second mapper to mapthe second bit stream may be a constellation in which a multilevelnumber in the first direction is smaller than a multilevel number in thesecond direction.

Accordingly, the transmission device can inhibit the influence of themultilevel number which increases due to superposition coding, for thefirst direction in which superposition coding is applied. Thus, thetransmission device can inhibit the influence of noise tolerance whichdecreases due to superposition coding, for the first direction in whichsuperposition coding is applied.

For example, the multiplexed signal generated by the superposer may be asignal on which (i) a first modulated symbol in the first modulatedsymbol stream, (ii) a first component that a second modulated symbol inthe second modulated symbol stream includes in the first direction, and(iii) a second component that the second modulated symbol includes inthe second direction are superposed, and a proportion of the firstcomponent superposed on the multiplexed signal may be lower than aproportion of the second component superposed on the multiplexed signal.

Accordingly, the transmission device relatively decreases the firstcomponent in the first direction in which superposition coding isapplied, and can relatively increase the second component in the seconddirection perpendicular to the first direction. Thus, the transmissiondevice can appropriately apply superposition coding for the firstcomponent, and inhibit the influence caused by superposition coding forthe second component.

For example, the converter may control a polarity of a component thateach of modulated symbols in the second modulated symbol stream includesin the first direction, by subjecting the second modulated symbol streamto the conversion, in superposing the first modulated symbol stream andthe second modulated symbol stream, the superposer may superpose a firstmodulated symbol in the first modulated symbol stream and a secondmodulated symbol in the second modulated symbol stream in which thepolarity is controlled, and in controlling the polarity, the convertermay reverse a polarity of a component that the second modulated symbolincludes in the first direction when the first modulated symbolcorresponds to one of two signal points adjacent to each other in thefirst constellation, and may maintain the polarity of the component thatthe second modulated symbol includes in the first direction when thefirst modulated symbol corresponds to the other of the two signalpoints.

Accordingly, the transmission device can appropriately control thepolarity of the component that the second modulated symbol in the secondmodulated symbol stream includes in the first direction, in accordancewith the first modulated symbol in the first modulated symbol stream.

A reception device according to an aspect of the present disclosureincludes: a receiver that receives a multiplexed signal into which aplurality of data series including a first data series in a first layerand a second data series in a second layer have been multiplexed, and onwhich a first modulated symbol stream and a second modulated symbolstream are superposed at a predetermined amplitude ratio, the firstmodulated symbol stream being generated by mapping a first bit stream ofthe first data series, the second modulated symbol stream beinggenerated by mapping a second bit stream of the second data series; anda deriver that derives at least one of the first data series or thesecond data series from the multiplexed signal. The multiplexed signalreceived by the receiver is a signal on which the first modulated symbolstream and the second modulated symbol stream are superposed, the secondmodulated symbol stream being subjected to conversion in accordance withthe first modulated symbol stream in only a first direction among thefirst direction and a second direction perpendicular to each other in acomplex plane in which the first modulated symbol stream and the secondmodulated symbol stream are represented.

Accordingly, the reception device can receive the multiplexed signalinto which the first modulated symbol stream and the second modulatedsymbol stream adjusted in accordance with the first modulated symbolstream with respect to the first direction in the complex plane aremultiplexed. Thus, the reception device can appropriately derive thefirst data series or the second data series from the multiplexed signalinto which the first data series and the second data series areappropriately multiplexed. Hence, the reception device can efficientlyperform processing in a multiplexing scheme that utilizes superpositioncoding.

A transmission method according to an aspect of the present disclosureis a transmission method of multiplexing a plurality of data seriesincluding a first data series in a first layer and a second data seriesin a second layer, and transmitting a multiplexed signal into which theplurality of data series have been multiplexed, the transmission methodincluding: mapping a first bit stream of the first data series togenerate a first modulated symbol stream of the first data series;mapping a second bit stream of the second data series to generate asecond modulated symbol stream of the second data series; subjecting thesecond modulated symbol stream to conversion in accordance with thefirst modulated symbol stream in only a first direction among the firstdirection and a second direction perpendicular to each other in acomplex plane in which the first modulated symbol stream and the secondmodulated symbol stream are represented; superposing the first modulatedsymbol stream and the second modulated symbol stream subjected to theconversion, at a predetermined amplitude ratio, to generate themultiplexed signal; and transmitting the multiplexed signal.

Accordingly, for example, the transmission device, etc. employing thistransmission method can convert the component that each modulated symbolin the second modulated symbol stream of the second data series includesin the first direction, in accordance with the first modulated symbolstream of the first data series. The transmission device, etc. employingthis transmission method thus can appropriately adjust the secondmodulated symbol stream of the second data series in accordance with thefirst modulated symbol stream of the first data series, and allow thesecond data series to be readily derived from the multiplexed signalinto which the first modulated symbol stream and the second modulatedsymbol stream are multiplexed.

Thus, the transmission device, etc. employing this transmission methodcan help inhibiting a processing delay in the reception device, and canefficiently perform processing in a multiplexing scheme that utilizessuperposition coding.

For example, a polarity of a component that each of modulated symbols inthe second modulated symbol stream includes in the first direction maybe controlled by the second modulated symbol stream being subjected tothe conversion.

Accordingly, the transmission device, etc. employing this transmissionmethod can control the polarity of a component that each modulatedsymbol in the second modulated symbol stream includes in the firstdirection, in accordance with the first modulated symbol stream. Thus,the transmission device, etc. employing this transmission method cansuperpose the first modulated symbol stream, and the second modulatedsymbol stream in which the polarity of each modulated symbol in thefirst direction is controlled in accordance with the first modulatedsymbol stream. Stated differently, the transmission device, etc.employing this transmission method can superpose the first modulatedsymbol stream, and the second modulated symbol stream in which thepolarity is appropriately adjusted in accordance with the firstmodulated symbol stream.

For example, in superposing the first modulated symbol stream and thesecond modulated symbol stream, a first modulated symbol in the firstmodulated symbol stream and a second modulated symbol in the secondmodulated symbol stream in which the polarity is controlled may besuperposed, and in controlling the polarity, when a component that thefirst modulated symbol includes in the first direction satisfies apredetermined condition, a polarity of a component that the secondmodulated symbol includes in the first direction may be reversed.

Thus, the transmission device, etc. employing this transmission methodcan transmit the multiplexed signal on which the first modulated symboland the second modulated symbol the polarity of which in the firstdirection is reversed in accordance with the first modulated symbol aresuperposed. The reversal of the polarity of the second modulated symbolbrings a plurality of signal points associated with the same bit groupof the second data series close to each other. Thus, the transmissiondevice, etc. employing this transmission method can more appropriatelyadjust the second modulated symbol stream of the second data series inaccordance with the first modulated symbol stream of the first dataseries, and allow the second data series to be readily derived from themultiplexed signal.

For example, the second modulated symbol stream may be subjected to theconversion by converting the second bit stream, a constellation used tomap the second bit stream, or the second modulated symbol stream, inaccordance with the first bit stream or the first modulated symbolstream.

Thus, the transmission device, etc. employing this transmission methodcan convert information corresponding to the second modulated symbolstream in accordance with information corresponding to the firstmodulated symbol stream, and can appropriately subject the secondmodulated symbol stream to the conversion in accordance with the firstmodulated symbol stream.

For example, in mapping the first bit stream, a first constellation maybe used to map the first bit stream, the first constellation being aconstellation in which a plurality of signal points are dispersed inonly the first direction among the first direction and the seconddirection, and in mapping the second bit stream, a second constellationmay be used to map the second bit stream, the second constellation beinga constellation in which a plurality of signal points are dispersed inboth the first direction and the second direction.

Accordingly, the transmission device, etc. employing this transmissionmethod can apply superposition coding in the first direction. Thus, thetransmission device, etc. employing this transmission method cansuperpose, onto a single component, a component that the first modulatedsymbol in the first modulated symbol stream includes in the firstdirection and a component that the second modulated symbol in the secondmodulated symbol stream includes in the first direction. Further, thetransmission device, etc. employing this transmission method can applysuitable superposition coding in the first direction, using the secondmodulated symbol stream adjusted with respect to the first direction.

For example, in mapping the second bit stream, the second constellationused to map the second bit stream may be a constellation in which noisetolerance in the first direction is higher than noise tolerance in thesecond direction.

Accordingly, the transmission device, etc. employing this transmissionmethod can inhibit the influence of noise tolerance that decreases dueto superposition coding, for the first direction in which superpositioncoding is applied.

For example, in mapping the second bit stream, the second constellationused to map the second bit stream may be a constellation in which amultilevel number in the first direction is smaller than a multilevelnumber in the second direction.

Accordingly, the transmission device, etc. employing this transmissionmethod can inhibit the influence of a multilevel number which increasesdue to superposition coding, for the first direction in whichsuperposition coding is applied. Specifically, the transmission device,etc. employing this transmission method can inhibit the influence ofnoise tolerance which decreases due to superposition coding, for thefirst direction in which superposition coding is applied.

For example, in generating the multiplexed signal, the multiplexedsignal generated may be a signal on which (i) a first modulated symbolin the first modulated symbol stream, (ii) a first component that asecond modulated symbol in the second modulated symbol stream includesin the first direction, and (iii) a second component that the secondmodulated symbol includes in the second direction are superposed, and aproportion of the first component superposed on the multiplexed signalmay be lower than a proportion of the second component superposed on themultiplexed signal.

Accordingly, the transmission device, etc. employing this transmissionmethod can make the first component in the first direction in whichsuperposition coding is applied relatively small and can make the secondcomponent in the second direction perpendicular to the first directionrelatively large. Thus, the transmission device, etc. employing thistransmission method can appropriately apply superposition coding to thefirst component, and can inhibit the influence caused by superpositioncoding on the second component.

For example, a polarity of a component that each of modulated symbols inthe second modulated symbol stream includes in the first direction maybe controlled by the second modulated symbol stream being subjected tothe conversion, in superposing the first modulated symbol stream and thesecond modulated symbol stream, a first modulated symbol in the firstmodulated symbol stream and a second modulated symbol in the secondmodulated symbol stream in which the polarity is controlled may besuperposed, and in controlling the polarity, a polarity of a componentthat the second modulated symbol includes in the first direction may bereversed when the first modulated symbol corresponds to one of twosignal points adjacent to each other in the first constellation, and thepolarity of the component that the second modulated symbol includes inthe first direction may be maintained when the first modulated symbolcorresponds to the other of the two signal points.

Accordingly, the transmission device, etc. employing this transmissionmethod can appropriately control the polarity of a component that thesecond modulated symbol in the second modulated symbol stream includesin the first direction, in accordance with the first modulated symbol inthe first modulated symbol stream.

A receiving method according to an aspect of the present disclosureincludes: receiving a multiplexed signal into which a plurality of dataseries including a first data series in a first layer and a second dataseries in a second layer have been multiplexed, and on which a firstmodulated symbol stream and a second modulated symbol stream aresuperposed at a predetermined amplitude ratio, the first modulatedsymbol stream being generated by mapping a first bit stream of the firstdata series, the second modulated symbol stream being generated bymapping a second bit stream of the second data series; and deriving atleast one of the first data series or the second data series from themultiplexed signal. In receiving the multiplexed signal, the multiplexedsignal received is a signal on which the first modulated symbol streamand the second modulated symbol stream are superposed, the secondmodulated symbol stream being subjected to conversion in accordance withthe first modulated symbol stream in only a first direction among thefirst direction and a second direction perpendicular to each other in acomplex plane in which the first modulated symbol stream and the secondmodulated symbol stream are represented.

Accordingly, the reception device, etc. employing this reception methodcan receive a multiplexed signal into which the first modulated symbolstream and the second modulated symbol stream adjusted in accordancewith the first modulated symbol stream with respect to the firstdirection in the complex plane are multiplexed. Accordingly, thereception device, etc. employing this reception method can appropriatelyderive the first data series or the second data series from themultiplexed signal into which the first data series and the second dataseries are appropriately multiplexed. Thus, the reception device, etc.employing this reception method can efficiently perform processing in amultiplexing scheme that utilizes superposition coding.

Note that although the above description of the embodiments illustratesan example in which two data series are multiplexed and transmitted onthe two layers to simplify the description, it is clear that the presentdisclosure is readily extendable to multiplexing and transmitting threeor more data series, following the embodiments.

Also, FIG. 1, FIG. 13 to FIG. 15, and FIG. 24 to FIG. 26 illustrate anexample in which a radio-frequency signal is sent from an externalantenna connected to the transmission device that does not include anantenna, but the transmission device may include an antenna such that aradio-frequency signal is sent from such an antenna of the transmissiondevice.

Also, FIG. 2, FIG. 7, FIG. 16 to FIG. 19, and FIG. 27 to FIG. 30illustrate an example in which a radio-frequency signal is sent from anexternal antenna connected to the reception device that does not includean antenna, but the reception device may include an antenna such that aradio-frequency signal is sent from such an antenna of the receptiondevice.

Also, the antennas used to send/receive a radio-frequency signal may bean antenna unit that includes a plurality of antennas.

Although not illustrated in FIG. 1, FIG. 13 to FIG. 15, and FIG. 24 toFIG. 26, the transmission device may include a frame configuration unitthat arranges a superposed signal generated by the adder in accordancewith a predetermined frame configuration to generate a frame, andoutputs such a frame into the RF unit.

Here, the configuration of a frame generated by the frame configurationunit may be uniform, or may be changed in accordance with a controlsignal sent from a controller not illustrated. The frame configurationunit arranges, in a frame, a superposed modulated symbol stream in whichthe first data series and the second data series are multiplexed, inaccordance with a predetermined rule.

The frame generated by the frame configuration unit may include a pilotsymbol, a control information symbol, a preamble, etc. in addition to adata symbol. Note that a pilot symbol, a control information symbol, anda preamble can each be referred to by another name.

For example, a pilot symbol may be a symbol that is generated by mappinga bit stream known to the reception device on the basis of PSKmodulation such as BPSK and QPSK. A pilot symbol may also be a symbolthat includes an amplitude and in-phase (or complex value) known to thereception device. A pilot symbol may also be a symbol, according towhich the reception device can estimate the amplitude and in-phase (orcomplex value) sent by the transmission device.

Then, the reception device uses the pilot symbol to perform frequencysynchronization, time synchronization, channel estimation, etc. on thereceived signal. Channel estimation is also referred to as theestimation of channel state information (CSI).

A control information symbol is a symbol used to transmit informationthat should be notified to the reception device as information requiredto demodulate a received signal and obtain a desired data series.

For example, the transmission device sends a control information symbolcorresponding to control information. The control information mayindicate the mapping (modulation) scheme and error control coding schemeused for each data series, the code rate and code length of the errorcontrol coding scheme, and the positions where the modulated symbols ofeach data series are arranged in a frame, etc. The reception devicedemodulates the control information symbol to obtain the controlinformation. The reception device then demodulates a data symbol on thebasis of the obtained control information to obtain the data series.

The control information may also include information used to control theoperations of an application, such as settings information for an upperlayer.

A preamble is a signal added at the leading end of a frame. For example,the reception device may receive a signal that includes a preamble toperform processes such as frame detection and frame synchronization onthe basis of the preamble. A preamble may also include a pilot symboland a control information symbol. A frame may also include not only apreamble but also a postamble, which is a signal added at the rear endof the frame.

The encoders use low density parity check (LDPC) coding, turbo coding,etc., for example, as the error control coding scheme. The encoders mayalso use another coding scheme.

The transmission devices illustrated in FIG. 1, FIG. 13 to FIG. 15, andFIG. 24 to FIG. 26 include their respective interleavers, but may notinclude interleavers as described above. In such a case, thetransmission device may input a bit stream generated by each encoderdirectly into each mapper or may perform a process different frominterleaving on the bit stream before inputting it into each mapper.When the transmission device does not include any interleavers, thereception devices illustrated in FIG. 2, FIG. 7, FIG. 16 to FIG. 19, andFIG. 27 to FIG. 30 may not include any deinterleavers.

The deinterleavers of the reception devices illustrated in FIG. 2, FIG.7, FIG. 16 to FIG. 19, and FIG. 27 to FIG. 30 perform permutation on thebasis of a permutation rule that is a reverse rule of the permutationrule used by the transmission side, but may perform an operationdifferent from such permutation. For example, each deinterleaver mayinput into the corresponding decoder a plurality of bit likelihoods of abit likelihood stream generated by the corresponding demapper in the bitorder required for decoding performed by the decoder.

In the above description, although superposition coding and thevariation of superposition coding are applied to wireless transmission,but the present disclosure is not limited to the application to wirelesstransmission, and thus may be applied to wired transmission, opticaltransmission, etc. and also to storage into a recording medium. Afrequency band used for transmission is not limited to a radio-frequencyband, and thus may be a baseband.

“A plurality of” used in the present disclosure is synonymous with “twoor more”. Ordinal numbers such as first, second, and third may beremoved from the expressions, replaced by other wording, or newly addedas appropriate.

Note that the devices, methods, etc. according to the present disclosureare not limited to the respective embodiments, and thus allow forvarious modifications for implementation. For example, in theembodiments, the technology of the present disclosure is implemented asa communication device (transmission device or reception device), butthe technology of the present disclosure is not limited to this, andthus may be implemented as software used to execute a communicationmethod (transmission method or reception method) executed by such acommunication device.

Also, two or more structural components of the transmission device orthe reception device may be integrated as a single structural component,and a single structural component may be divided into two or morestructural components. Also, the transmission device and the receptiondevice may form a single transmission/reception device. In such a case,a plurality of structural components of the same kind may be integratedinto a single structural component. For example, a transmission antennaand a reception antenna may be formed by a single antenna.

Also, for example, a process performed by a specified structuralcomponent may be performed by another structural component. The order ofperforming processes may be changed, and a plurality of processes may beperformed in parallel.

Note that a program for executing the above-described communicationmethod may be previously stored in a read only memory (ROM) to beexecuted by a central processing unit (CPU).

Moreover, the program for executing the above communication method maybe stored in a computer-readable recording medium. Such a program storedin the recording medium may be recorded in a random access memory (RAM)in a computer so that the computer may execute the communication methodaccording to the program.

Note that each of the structural components according to theembodiments, etc. may be implemented as a large-scale integration (LSI),which is typically an integrated circuit. The structural components maytake the form of individual chips, or one or more or all of thestructural components according to the embodiments may be encapsulatedinto a single chip. Although LSI is illustrated here as an example, suchchips may be referred to as integrated circuits (ICs), system LSIs,super LSIs, or ultra LSIs, depending on their degree of integration.

The ICs are not limited to LSIs. Each of the structural components thusmay be implemented as a dedicated circuit or a general-purposeprocessor. A field programmable gate array (FPGA) that allows forprogramming after the manufacture of an LSI, or a reconfigurableprocessor that allows for reconfiguration of the connection and thesettings of circuit cells inside an LSI may be employed.

Furthermore, when the progress in a semiconductor technology or anotherderivative technology results in a new IC technology that replaces LSI,such new technology may of course be employed to integrate the devicesor some of their structural components according to the embodiments. Forexample, adaptation to biotechnology is possible.

Furthermore, when the progress in a semiconductor technology or anotherderivative technology results in a new IC technology that replaces LSI,such new technology may of course be employed to integrate the devicesor some of their structural components according to the embodiments. Forexample, adaptation to biotechnology is possible.

In this disclosure, the phrase of “at least one of A or B” should beinterpreted that the phrase includes only A, only B, and both A and B.

Although only some exemplary embodiments of the present disclosure havebeen described in detail above, those skilled in the art will readilyappreciate that many modifications are possible in the exemplaryembodiments without materially departing from the novel teachings andadvantages of the present disclosure. Accordingly, all suchmodifications are intended to be included within the scope of thepresent disclosure.

INDUSTRIAL APPLICABILITY

The present disclosure is applicable to a wireless communication systemand a broadcasting system, etc. The present disclosure is widelyapplicable to a system for multiplexing a plurality of data series bysuperposition coding.

The present disclosure is also applicable to a wired communicationsystem, etc. such as a power line communication (PLC) system, an opticalcommunication system, and a digital subscriber line (DSL) system. Thepresent disclosure is further applicable to a storage system, etc. forrecording data into a recording medium such as an optical disk and amagnetic disk.

What is claimed is:
 1. A reception device comprising: a receiverconfigured to receive, via a reception antenna, a multiplexed signal onwhich a first signal and a second signal are superposed at an amplituderatio, the first signal having a first in-phase component and a firstorthogonal component, the second signal having a second in-phasecomponent and a second orthogonal component, the second signal havingbeen subjected to QPSK modulation, the second signal having beenconverted to generate the multiplexed signal such that: (i) a polarityof the second in-phase component is inverted if a polarity of the firstin-phase component is positive; and (ii) a polarity of the secondorthogonal component is inverted if a polarity of the first orthogonalcomponent is positive; and a signal processing circuit configured toderive at least one of the first signal or the second signal from themultiplexed signal.
 2. The reception device according to claim 1,wherein in the multiplexed signal, the polarity of the second in-phasecomponent and the second orthogonal component have been controlledaccording to an equation into which the first in-phase component and thefirst orthogonal component are input as arguments.